Semiconductor nanocrystals, methods for making same, compositions, and products

ABSTRACT

A semiconductor nanocrystal characterized by having a solid state photoluminescence external quantum efficiency at a temperature of 90° C. or above that is at least 95% of the solid state photoluminescence external quantum efficiency of the semiconductor nanocrystal at 25° C. is disclosed. A semiconductor nanocrystal having a multiple LO phonon assisted charge thermal escape activation energy of at least 0.5 eV is also disclosed. A semiconductor nanocrystal capable of emitting light with a maximum peak emission at a wavelength in a range from 590 nm to 650 nm characterized by an absorption spectrum, wherein the absorption ratio of OD at 325 nm to OD at 450 nm is greater than 5.5. A semiconductor nanocrystal capable of emitting light with a maximum peak emission at a wavelength in a range from 545 nm to 590 nm characterized by an absorption spectrum, wherein the absorption ratio of OD at 325 nm to OD at 450 nm is greater than 7. A semiconductor nanocrystal capable of emitting light with a maximum peak emission at a wavelength in a range from 495 nm to 545 nm characterized by an absorption spectrum, wherein the absorption ratio of OD at 325 nm to OD at 450 nm is greater than 10. A composition comprising a plurality of semiconductor nanocrystals wherein the solid state photoluminescence efficiency of the composition at a temperature of 90° C. or above is at least 95% of the solid state photoluminescence efficiency of the composition 25° C. is further disclosed. A method for preparing semiconductor nanocrystals comprises introducing one or more first shell chalcogenide precursors and one or more first shell metal precursors to a reaction mixture including semiconductor nanocrystal cores, wherein the first shell chalcogenide precursors are added in an amount greater than the first shell metal precursors by a factor of at least about 2 molar equivalents and reacting the first shell precursors at a first reaction temperature of at least 300° C. to form a first shell on the semiconductor nanocrystal cores. Populations, compositions, components and other products including semiconductor nanocrystals of the invention are disclosed. Populations, compositions, components and other products including semiconductor nanocrystals made in accordance with any method of the invention is also disclosed.

This application is a continuation of International Application No.PCT/US2012/066154, filed 20 Nov. 2012, which was published in theEnglish language as International Publication No. WO 2013/115898 on 8Aug. 2013, which International Application claims priority to U.S.Provisional Patent Application No. 61/595,116, filed on 5 Feb. 2012 andU.S. Provisional Patent Application No. 61/678,902, filed on 2 Aug.2012. Each of the foregoing is hereby incorporated herein by referencein its entirety for all purposes.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to technical field of semiconductornanocrystals, including methods, and compositions and products includingsame.

BACKGROUND OF THE INVENTION

The solid state photoluminescence external quantum efficiency ofsemiconductor nanocrystals have been observed to be adversely affectedduring use by at least the temperature of the environment in which thenanocrystals are used. It would represent an advance in the art toprovide a semiconductor nanocrystal and a method for makingsemiconductor nanocrystals which address the adverse effect of theenvironmental temperature on solid state photoluminescence externalquantum efficiency of semiconductor nanocrystals.

SUMMARY OF THE INVENTION

The present invention relates to a semiconductor nanocrystal, methodsfor preparing semiconductor nanocrystals, and to compositions,components, and other products including semiconductor nanocrystalsdescribed herein and/or those prepared in accordance with any of themethods described herein.

In accordance with one aspect of the present invention, there isprovided a semiconductor nanocrystal characterized by having a solidstate photoluminescence external quantum efficiency at a temperature of90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

In accordance with another aspect of the present invention, there isprovided a semiconductor nanocrystal having a multiple LO phononassisted charge thermal escape activation energy of at least 0.5 eV.

As used herein, a multiple LO phonon assisted charge thermal escapeactivation energy refers to multiple LO phonon assisted charge thermalescape activation energy as determined with reference to the followingequation:I(T)=I ₀[1+A exp(−E/kT)]⁻¹wherein A is a constant, k=1.38×10⁻²³ Joules/Kelvin, T is temperature(Kelvin), and E is a value of the multiple LO phonon assisted chargethermal escape activation energy obtained by measuring solid statephotoluminescence external quantum efficiency of the nanocrystal as afunction of temperature and plotting ln [I_(o)/I(T)−1] vs. 1/kT whereI_(o) is the integrated photoluminescence (PL) intensity of thenanocrystal at room temperature and I(T) is the integrated PL intensityof the nanocrystal at temperature (T) where T spans from 70° C. to 140°C., and the absolute value of the slope of the line is the value of theactivation energy.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal characterized by having a solidstate photoluminescence external quantum efficiency of at least 80% at atemperature of 90° C. or above.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal characterized by having a radiativelifetime at a temperature of 90° C. or above that is at least 80% of theradiative lifetime at 25° C.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal capable of emitting light with amaximum peak emission at a wavelength in a range from 590 nm to 650 nmcharacterized by an absorption spectrum, wherein the absorption ratio ofOptical Density (OD) at 325 nm to OD at 450 nm is greater than 5.5.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal capable of emitting light with amaximum peak emission at a wavelength in a range from 545 nm to 590 nmcharacterized by an absorption spectrum, wherein the absorption ratio ofOD at 325 nm to OD at 450 nm is greater than 7.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal capable of emitting light with amaximum peak emission at a wavelength in a range from 495 nm to 545 nmcharacterized by an absorption spectrum, wherein the absorption ratio ofOD at 325 nm to OD at 450 nm is greater than 10.

In accordance with a further aspect of the present invention, there isprovided a composition comprising a plurality of semiconductornanocrystals wherein the solid state photoluminescence efficiency of thecomposition at a temperature of 90° C. or above is at least 95% of thesolid state photoluminescence efficiency of the composition at 25° C.

In accordance with yet a further aspect of the present invention, thereis provided a composition comprising a host material and a plurality ofsemiconductor nanocrystals wherein the solid state photoluminescenceefficiency of the composition is at least 80% at a temperature of 90° C.or above.

In accordance with a still further aspect of the present invention,there is provided a composition including at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided an optical material comprising at least onesemiconductor nanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a light emitting material comprising at least onesemiconductor nanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a color-conversion material comprising at least onesemiconductor nanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided an ink comprising at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a paint comprising at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a taggant comprising at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided an optical component including at least onesemiconductor nanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a backlighting unit including at least onesemiconductor nanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a display including at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided an electronic device including at least onesemiconductor nanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided an opto-electronic device including at least onesemiconductor nanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a light-emitting device including at least onesemiconductor nanocrystal described herein.

In certain embodiments, a light emitting device includes a lightemitting material comprising at least one semiconductor nanocrystaldescribed herein.

In accordance with a still further aspect of the present invention,there is provided a lamp including at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a light bulb including at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a luminaire including at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a method for preparing semiconductor nanocrystalscomprising: introducing one or more first shell chalcogenide precursorsand one or more first shell metal precursors to a reaction mixtureincluding semiconductor nanocrystal cores, wherein the first shellchalcogenide precursors are added in an amount greater than the firstshell metal precursors by a factor of at least about 2 molar equivalentsand reacting the first shell precursors at a first reaction temperatureof at least 300° C. to form a first shell on the semiconductornanocrystal cores.

In certain embodiments, the method further comprises: introducing one ormore second shell chalcogenide precursors and one or more second shellmetal precursors to the reaction mixture including semiconductornanocrystal cores including the first shell at a second reactiontemperature of at least 300° C., wherein the second shell chalcogenideprecursors are added in an amount of at least 0.7 molar equivalents ofthe second shell metal precursors, and reacting the second shellprecursors to form a second shell over the first shell on thesemiconductor nanocrystal cores.

In accordance with yet another aspect of the present invention, there isprovided a population of semiconductor nanocrystals prepared inaccordance with any of the methods described herein.

In accordance with a still further aspect of the present invention,there is provided a composition including at least one semiconductornanocrystal prepared in accordance with any of the methods describedherein.

In accordance with a still further aspect of the present invention,there is provided an optical material comprising at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In accordance with a still further aspect of the present invention,there is provided a light emitting material comprising at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In accordance with a still further aspect of the present invention,there is provided a color-conversion material comprising at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In accordance with a still further aspect of the present invention,there is provided an ink comprising at least one semiconductornanocrystal prepared in accordance with any of the methods describedherein.

In accordance with a still further aspect of the present invention,there is provided a paint comprising at least one semiconductornanocrystal prepared in accordance with any of the methods describedherein.

In accordance with a still further aspect of the present invention,there is provided a taggant comprising at least one semiconductornanocrystal prepared in accordance with any of the methods describedherein.

In accordance with a still further aspect of the present invention,there is provided an optical component including at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In accordance with a still further aspect of the present invention,there is provided a backlighting unit including at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In accordance with a still further aspect of the present invention,there is provided a display including at least one semiconductornanocrystal prepared in accordance with any of the methods describedherein.

In accordance with a still further aspect of the present invention,there is provided an electronic device including at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In accordance with a still further aspect of the present invention,there is provided an opto-electronic device including at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In accordance with a still further aspect of the present invention,there is provided a light-emitting device including at least onesemiconductor nanocrystal prepared in accordance with any of the methodsdescribed herein.

In certain embodiments, a light emitting device includes a lightemitting material comprising at least one semiconductor nanocrystalprepared in accordance with any of the methods described herein.

In accordance with a still further aspect of the present invention,there is provided a lamp including at least one semiconductornanocrystal described herein.

In accordance with a still further aspect of the present invention,there is provided a light bulb including at least one semiconductornanocrystal prepared in accordance with any of the methods describedherein.

In accordance with a still further aspect of the present invention,there is provided a luminaire including at least one semiconductornanocrystal prepared in accordance with any of the methods describedherein.

In accordance with certain aspects, oxygen and/or water may degradesemiconductor nanocrystals or quantum dots described herein duringperiods of high light flux exposure.

The foregoing, and other aspects and embodiments described herein allconstitute embodiments of the present invention.

It should be appreciated by those persons having ordinary skill in theart(s) to which the present invention relates that any of the features,described herein in respect of any particular aspect and/or embodimentof the present invention can be combined with one or more of any of theother features of any other aspects and/or embodiments of the presentinvention described herein, with modifications as appropriate to ensurecompatibility of the combinations. Such combinations are considered tobe part of the present invention contemplated by this disclosure.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention as claimed. Other embodimentswill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIGS. 1A and 1B graphically illustrate EQE (calculated from PLmeasurements) vs. Temperature for examples of embodiments of the presentinvention and for control samples.

FIGS. 2A and 2B graphically illustrate a plot of integrated PL (Σ_(PL))vs. temperature showing the % drop in PL vs. temperature for examples ofembodiments of the present invention and for control samples.

FIGS. 3A and 3B graphically illustrate ln [I_(o)/I(T)−1] vs. 1/kT forexamples of embodiments of the present invention and for controlsamples.

FIGS. 4A and 4B graphically illustrate absorption profiles and 325nm/450 nm Ratios for examples of embodiments of the present inventionand for control samples.

FIGS. 5A and 5B graphically illustrate Absorption spectra referred to inExamples 1A and 1B.

FIGS. 6A and 6B graphically illustrate absorption and emission spectrareferred to in Examples 1A and 1B.

FIG. 7 graphically illustrate EQE (calculated from PL measurements) vs.Temperature for an example of an embodiment of the present invention andfor a control sample.

FIGS. 8A and 8B graphically illustrate absorption and emission spectrareferred to in Examples 10A and 10B.

FIGS. 9A and 9B graphically illustrate absorption and emission spectrareferred to in Examples 11A and 11B.

The attached figures are simplified representations presented forpurposes of illustration only; the actual structures may differ innumerous respects, particularly including the relative scale of thearticles depicted and aspects thereof.

For a better understanding to the present invention, together with otheradvantages and capabilities thereof, reference is made to the followingdisclosure and appended claims in connection with the above-describeddrawings.

DETAILED DESCRIPTION OF THE INVENTION

Various aspects and embodiments of the present inventions will befurther described in the following detailed description.

The present invention relates to a semiconductor nanocrystals, methodsfor making and overcoating semiconductor nanocrystals, and tocompositions, components, and other products including semiconductornanocrystals described herein and/or those prepared in accordance withany of the methods described herein.

In accordance with one aspect of the present invention, there isprovided a semiconductor nanocrystal characterized by having a solidstate photoluminescence external quantum efficiency at a temperature of90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence efficiency at the temperature of 90° C. or above thatis from 95 to 100% of the solid state photoluminescence efficiency at25° C.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In accordance with another aspect of the present invention, there isprovided semiconductor nanocrystal having a multiple LO phonon assistedcharge thermal escape activation energy of at least 0.5 eV.

As set forth above, a multiple LO phonon assisted charge thermal escapeactivation energy refers to multiple LO phonon assisted charge thermalescape activation energy as determined with reference to the followingequation:I(T)=I ₀[1+A exp(−E/kT)]⁻¹wherein A is a constant and E is a value of the multiple LO phononassisted charge thermal escape activation energy obtained by measuringsolid state photoluminescence external quantum efficiency of thenanocrystal as a function of temperature and plotting ln [I_(o)/I(T)−1]vs. 1/kT where I_(o) is the integrated photoluminescence (PL) intensityof the nanocrystal at room temperature and I(T) is the integrated PLintensity of the nanocrystal at temperature (T) where T spans from 70°C. to 140° C., and the absolute value of the slope of the line is thevalue of the activation energy.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 80% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 85% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 90% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 95% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency from 95% to 100% at atemperature of 90° C. or above.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the semiconductor nanocrystal is characterizedby having a solid state photoluminescence external quantum efficiency ata temperature of 90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

In accordance with another aspect of the present invention, there isprovided a semiconductor nanocrystal characterized by having a radiativelifetime at a temperature of 90° C. or above that is at least 80% of theradiative lifetime at 25° C.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the semiconductor nanocrystal has a radiativelifetime at the temperature of 90° C. or above that is at least 90% ofthe radiative lifetime at 25° C.

In certain embodiments, the semiconductor nanocrystal has a radiativelifetime at the temperature of 90° C. or above that is at least 95% ofthe radiative lifetime at 25° C.

In certain embodiments, the semiconductor nanocrystal has a radiativelifetime at the temperature of 90° C. or above that is from 95 to 100%of the radiative lifetime at 25° C.

In certain embodiments, the semiconductor nanocrystal is characterizedby having a solid state photoluminescence external quantum efficiency ata temperature of 90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal capable of emitting light with amaximum peak emission at a wavelength in a range from 590 nm to 650 nmcharacterized by an absorption spectrum, wherein the absorption ratio ofOD at 325 nm to OD at 450 nm is greater than 5.5.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 80% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 85% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 90% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 95% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency from 95% to 100% at atemperature of 90° C. or above.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the semiconductor nanocrystal is characterizedby having a solid state photoluminescence external quantum efficiency ata temperature of 90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal capable of emitting light with amaximum peak emission at a wavelength in a range from 545 nm to 590 nmcharacterized by an absorption spectrum, wherein the absorption ratio ofOD at 325 nm to OD at 450 nm is greater than 7.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 80% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 85% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 90% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 95% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency from 95% to 100% at atemperature of 90° C. or above.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the semiconductor nanocrystal is characterizedby having a solid state photoluminescence external quantum efficiency ata temperature of 90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

In accordance with a further aspect of the present invention, there isprovided a semiconductor nanocrystal capable of emitting light with amaximum peak emission at a wavelength in a range from 495 nm to 545 nmcharacterized by an absorption spectrum, wherein the absorption ratio ofOD at 325 nm to OD at 450 nm is greater than 10.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 80% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 85% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 90% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 95% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency from 95% to 100% at atemperature of 90° C. or above.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the semiconductor nanocrystal is characterizedby having a solid state photoluminescence external quantum efficiency ata temperature of 90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

In accordance with another aspect of the present invention there isprovided a semiconductor nanocrystal characterized by having a solidstate photoluminescence external quantum efficiency of at least 80% at atemperature of 90° C. or above.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 85% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 90% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency of at least 95% at atemperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal has a solid statephotoluminescence external quantum efficiency that is from 95 to 100% ata temperature of 90° C. or above.

In certain embodiments, the semiconductor nanocrystal is characterizedby having a solid state photoluminescence external quantum efficiency ata temperature of 90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.

Semiconductor nanocrystals are nanometer sized semiconductor particlesthat can have optical properties arising from quantum confinement. Theparticular composition(s), structure, and/or size of a semiconductornanocrystal can be selected to achieve the desired wavelength of lightto be emitted from the semiconductor nanocrystal upon excitation. Inessence, semiconductor nanocrystals may be tuned to emit light acrossthe visible spectrum by changing their size. See C. B. Murray, C. R.Kagan, and M. G. Bawendi, Annual Review of Material Sci., 2000, 30:545-610 hereby incorporated by reference in its entirety. The narrowFWHM of semiconductor nanocrystals can result in saturated coloremission. In certain embodiments, FWHM can be, for example, less than60, less than 50, less than 40, or less than 30. The broadly tunable,saturated color emission over the entire visible spectrum of a singlematerial system is unmatched by any class of organic chromophores (see,for example, Dabbousi et al., J. Phys. Chem. 101, 9463 (1997), which isincorporated by reference in its entirety). A monodisperse population ofsemiconductor nanocrystals will emit light spanning a narrow range ofwavelengths.

A semiconductor nanocrystal in accordance with the present invention cancomprise one or more inorganic semiconductor materials that can berepresented by the formula MX, where M is a metal from a metal donor andX is a compound from an X donor which is capable of reacting with themetal donor to form a material with the general formula MX. In certainembodiments, the M donor and the X donor can be moieties within the samemolecule. The M donor can be an inorganic compound, an organometalliccompound, or elemental metal. For example, an M donor can comprisecadmium, zinc, magnesium, mercury, aluminum, gallium, indium orthallium, and the X donor can comprise a compound capable of reactingwith the M donor to form a material with the general formula MX.Exemplary metal precursors include dimethylcadmium and cadmium oleate.The X donor can comprise a chalcogenide donor or a pnictide donor, suchas a phosphine chalcogenide, a bis(silyl) chalcogenide, dioxygen, anammonium salt, or a tris(silyl) pnictide. Suitable X donors include, forexample, but are not limited to, dioxygen, bis(trimethylsilyl) selenide((TMS)₂Se), trialkyl phosphine selenides such as (tri-noctylphosphine)selenide (TOPSe) or (tri-n-butylphosphine) selenide (TBPSe), trialkylphosphine tellurides such as (tri-n-octylphosphine) telluride (TOPTe) orhexapropylphosphorustriamide telluride (HPPTTe),bis(trimethylsilyl)telluride ((TMS)₂Te), bis(trimethylsilyl)sulfide((TMS)₂S), a trialkyl phosphine sulfide such as (tri-noctylphosphine)sulfide (TOPS), an ammonium salt such as an ammonium halide (e.g.,NH₄Cl), tris(trimethylsilyl)phosphide ((TMS)₃P),tris(trimethylsilyl)arsenide ((TMS)₃As), ortris(trimethylsilyl)antimonide ((TMS)₃Sb). In certain embodiments, the Mdonor and the X donor can be moieties within the same molecule.

As mentioned above, a semiconductor nanocrystal can comprise one or moresemiconductor materials. Examples of semiconductor materials that can beincluded in a semiconductor nanocrystal (including, e.g., semiconductornanocrystal) include, but are not limited to, a Group IV element, aGroup II-VI compound, a Group II-V compound, a Group III-VI compound, aGroup III-V compound, a Group IV-VI compound, a Group compound, a GroupII-IV-VI compound, a Group II-IV-V compound, an alloy including any ofthe foregoing, and/or a mixture including any of the foregoing,including ternary and quaternary mixtures or alloys. A non-limiting listof examples include ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS,MgSe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP,InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe,Ge, Si, an alloy including any of the foregoing, and/or a mixtureincluding any of the foregoing, including ternary and quaternarymixtures or alloys.

In certain preferred embodiments, a semiconductor nanocrystal inaccordance with the present invention can comprise a core comprising oneor more semiconductor materials and a shell comprising one or moresemiconductor materials, wherein the shell is disposed over at least aportion, and preferably all, of the outer surface of the core. Asemiconductor nanocrystal including a core and shell is also referred toas a “core/shell” structure.

For example, a semiconductor nanocrystal can include a core having theformula MX, where M is cadmium, zinc, magnesium, mercury, aluminum,gallium, indium, thallium, or mixtures thereof, and X is oxygen, sulfur,selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, ormixtures thereof. Examples of materials suitable for use assemiconductor nanocrystal cores include, but are not limited to, ZnO,ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS, MgSe, GaAs, GaN, GaP, GaSe,GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP, InSb, AlAs, AlN, AlP, AlSb,TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe, Ge, Si, an alloy includingany of the foregoing, and/or a mixture including any of the foregoing,including ternary and quaternary mixtures or alloys.

A shell can be a semiconductor material having a composition that is thesame as or different from the composition of the core. The shell cancomprise an overcoat including one or more semiconductor materials on asurface of the core. Examples of semiconductor materials that can beincluded in a shell include, but are not limited to, a Group IV element,a Group II-VI compound, a Group II-V compound, a Group III-VI compound,a Group III-V compound, a Group IV-VI compound, a Group compound, aGroup II-IV-VI compound, a Group II-IV-V compound, alloys including anyof the foregoing, and/or mixtures including any of the foregoing,including ternary and quaternary mixtures or alloys. Examples include,but are not limited to, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS,MgSe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP,InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO, PbS, PbSe, PbTe,Ge, Si, an alloy including any of the foregoing, and/or a mixtureincluding any of the foregoing. For example, ZnS, ZnSe or CdSovercoatings can be grown on CdSe or CdTe semiconductor nanocrystals.

In a core/shell semiconductor nanocrystal, the shell or overcoating maycomprise one or more layers. The overcoating can comprise at least onesemiconductor material which is the same as or different from thecomposition of the core. An overcoating can have a thickness from aboutone to about ten monolayers. An overcoating can also have a thicknessgreater than ten monolayers. In certain embodiments, more than oneovercoating can be included on a core. By adjusting the temperature ofthe reaction mixture during overcoating and monitoring the absorptionspectrum of the core, overcoated materials having high emission quantumefficiencies and narrow size distributions can be obtained.

In certain embodiments, the surrounding “shell” material can have a bandgap greater than the band gap of the core material. In certain otherembodiments, the surrounding shell material can have a band gap lessthan the band gap of the core material.

In certain preferred embodiments, a core/shell semiconductor nanocrystalhas a Type I structure.

In certain embodiments, a shell can be chosen so as to have an atomicspacing close to that of the underlying “core” or shell (e.g., latticeconstants that are within up to 13% of each other, and preferably withinup to 10% of each other). In certain other embodiments, the shell andcore materials can have the same crystal structure.

Examples of semiconductor nanocrystal core/shell structures include,without limitation: red (e.g., CdSe/CdZnS (core/shell); CdSe/ZnS/CdZnS(core/shell/shell), etc.) green (e.g., CdZnSe/CdZnS (core/shell),CdSe/ZnS/CdZnS (core/shell/shell), etc.), and blue (e.g., CdS/CdZnS(core/shell)).

Semiconductor nanocrystals can have various shapes, including, but notlimited to, a sphere, rod, disk, other shapes, and mixtures of variousshaped particles.

In certain preferred embodiments of the various aspects of theinventions described herein, the semiconductor nanocrystal is undoped.

As used herein, “undoped semiconductor nanocrystal” refers to asemiconductor nanocrystal that emits light due to quantum confinementand without emission from an activator species.

In certain preferred embodiments of the various aspects of the inventiondescribed herein, the semiconductor nanocrystal includes a corecomprising a first semiconductor material and at least a first shellsurrounding the core, wherein the first shell comprises a secondsemiconductor material. In certain of such embodiments, the first shellhas a thickness greater than or equal to the thickness of 1 monolayer ofthe second semiconductor material. In certain of such embodiments, thefirst shell has a thickness up to the thickness of about 10 monolayersof the second semiconductor material.

In certain of such preferred embodiments, the semiconductor nanocrystalcan include a second shell surrounding the outer surface thereof. Incertain of such embodiments, the second shell can comprise a thirdsemiconductor material.

In certain of such preferred embodiments wherein the semiconductornanocrystal includes a second shell, the second shall can have athickness greater than or equal to the thickness of 3 monolayers of thematerial from which it is constituted, e.g., the third semiconductormaterial. In certain of such embodiments, the second shell can have athickness up to the thickness of about 20 monolayers of the materialfrom which it is constituted.

In certain more preferred embodiments, the second semiconductor materialincluded in the first shell comprises zinc sulfide, and the second shellcomprises a third semiconductor material including one or more metalswherein the one or metals comprises from 0 to less than 100% cadmium.

In one example of a preferred embodiment, the semiconductor nanocrystalincludes a core comprising CdSe having a predetermined size, a firstshell comprising ZnS at a thickness of about 3-4 monolayers of ZnS, anda second shell comprises Cd_(1-x)Zn_(x)S wherein 0<x≤1 at a thickness ofabout 9-10 monolayers of Cd_(1-x)Zn_(x)S.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal can include a core comprising afirst semiconductor material, a first shell comprising a secondsemiconductor material, and a second shell comprising a thirdsemiconductor material, wherein the first shell has a bandgap which isgreater than that of the second shell.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal can include a core comprising afirst semiconductor material, a first shell comprising a secondsemiconductor material, and a second shell comprising a thirdsemiconductor material, wherein the first shell has a bandgap which isgreater than that of the second shell, and the bandgap of the firstshell is also greater than that of the core.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal can include a core comprising afirst semiconductor material, a first shell comprising a secondsemiconductor material, a second shell comprising third semiconductormaterial, and a third shell comprising a fourth semiconductor material,wherein the third shell has a bandgap that is the same as that of thefirst shell and the second shell has a bandgap that is less than that ofthe first shell.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal can include a core comprising afirst semiconductor material, a first shell comprising a secondsemiconductor material, wherein the core has a bandgap which differsfrom that of the first shell by at least 0.8 eV.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal can include a core comprising afirst semiconductor material, a first shell comprising a secondsemiconductor material, wherein the core has a bandgap which differsfrom that of the first shell by at least 1 eV.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal can include a core comprising afirst semiconductor material, the core having a first conduction bandenergy (E_(CB)), and a first shell comprising a second semiconductormaterial, the first shell having a second conduction band energy(E_(CB)), wherein the absolute value of the difference between E_(CB) ofthe core and E_(CB) of the first shell multiplied by the total shellthickness (nm) surrounding the core in the nanocrystal is greater than 2eV*nm. In certain embodiments, the absolute value of the differencebetween E_(CB) of the core and E_(CB) of the first shell multiplied bythe total shell thickness (nm) surrounding the core in the nanocrystalis greater than 3 eV*nm. In certain embodiments, the absolute value ofthe difference between E_(CB) of the core and E_(CB) of the first shellmultiplied by the total shell thickness (nm) surrounding the core in thenanocrystal is greater than 4 eV*nm. In embodiments including more thanone shell, total shell thickness is the total thickness of all shellssurrounding the core.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal can include a core comprising afirst semiconductor material, the core having a first valence bandenergy (E_(VB)), and a first shell comprising a second semiconductormaterial, the first shell having a second valence band energy (E_(VB)),wherein the absolute value of the difference between E_(VB) of the coreand E_(VB) of the first shell multiplied by the total shell thickness(nm) surrounding the core in the nanocrystal is greater than 2 eV*nm. Incertain embodiments, the absolute value of the difference between E_(VB)of the core and E_(VB) of the first shell multiplied by the total shellthickness (nm) surrounding the core in the nanocrystal is greater than 3eV*nm. In certain embodiments, the absolute value of the differencebetween E_(VB) of the core and E_(VB) of the first shell multiplied bythe total shell thickness (nm) surrounding the core in the nanocrystalis greater than 4 eV*nm. In embodiments including more than one shell,total shell thickness is the total thickness of all shells surroundingthe core.

In certain embodiments of the various aspects of the invention describedherein, the semiconductor nanocrystal including a first shell and asecond shell can further include one or more additional shells on theouter surface of the nanocrystal. Any of such additional shells canpartially or fully surround the outer surface of the nanocrystal onwhich it is disposed. Preferably an additional shell fully surrounds theouter surface.

In certain preferred embodiments, the semiconductor nanocrystals areprepared in accordance with a method described herein.

Semiconductor nanocrystals (also referred to as quantum dots) preferablyhave ligands attached thereto. Semiconductor nanocrystals within thescope of the present invention include, without limitation, green CdSesemiconductor nanocrystals having oleic acid ligands and red CdSesemiconductor nanocrystals having oleic acid ligands. Alternatively, orin addition, octadecylphosphonic acid (“ODPA”) ligands may be usedinstead of, or in addition to, oleic acid ligands. The ligands canfacilitate dispersibility of the nanocrystals in a medium.

Ligands can be derived from a coordinating solvent that may be includedin the reaction mixture during the growth process. Ligands can be addedto the reaction mixture. Ligands can be derived from a reagent orprecursor included in the reaction mixture for synthesizing thesemiconductor nanocrystals. Ligands can be exchanged with ligands on thesurface of a semiconductor nanocrystal. In certain embodiments,semiconductor nanocrystals can include more than one type of ligandattached to an outer surface.

In certain embodiments of the various aspects of the inventionsdescribed herein, semiconductor nanocrystals can include aliphaticligands attached thereto. According to one aspect, exemplary ligandsinclude oleic acid ligands and octadecylphosphonic acid (“ODPA”)ligands.

Ligands can be selected based on the particular end-use application inwhich the semiconductor nanocrystals are to be included. Such selectionis within the skill of the person of ordinary skill in the relevant art.

The emission from a semiconductor nanocrystal capable of emitting lightcan be a narrow Gaussian emission band that can be tuned through thecomplete wavelength range of the ultraviolet, visible, or infra-redregions of the spectrum by varying the size of the semiconductornanocrystal, the composition of the semiconductor nanocrystal, and/orthe structure of the semiconductor nanocrystal (e.g., core, core/shell,core/shell/shell, and other structural variations). For example, asemiconductor nanocrystal comprising CdSe can be tuned in the visibleregion; a semiconductor nanocrystal comprising InAs can be tuned in theinfra-red region. The narrow size distribution of a population ofsemiconductor nanocrystals capable of emitting light can result inemission of light in a narrow spectral range. The population can bemonodisperse preferably exhibits less than a 15% rms (root-mean-square)deviation in diameter of such semiconductor nanocrystals, morepreferably less than 10%, most preferably less than 5%.

Semiconductor nanocrystals of the present invention can have spectralemissions in a narrow range of no greater than about 75 nm, for example,no greater than about 70, no greater than about 60 nm, preferably nogreater than about 50 nm, more preferably no greater than about 40 nm,and most preferably no greater than about 30 nm full width at halfmaximum (FWHM) for such semiconductor nanocrystals that emit in thevisible region of the electromagnetic spectrum. In certain embodiments,spectral emissions in a narrow range of no greater than about 25 nm(e.g., no greater than about 20 nm, or no greater than about 15 nm), canbe preferred. IR-emitting semiconductor nanocrystals can have a FWHM ofno greater than 150 nm, or no greater than 100 nm. Expressed in terms ofthe energy of the emission, the emission can have a FWHM of no greaterthan 0.05 eV, or no greater than 0.03 eV. The breadth of the emissiondecreases as the dispersity of the light-emitting semiconductornanocrystal diameters decreases.

A semiconductor nanocrystal in accordance with the present invention canemit light in a predetermined spectral region. As discussed above,tuning the emission to fall within a predetermined spectral region canbe achieved by selection of the size of the semiconductor nanocrystal,the composition of the semiconductor nanocrystal, and/or the structureof the semiconductor nanocrystal, which is within the skill or theperson of ordinary skill in the art.

In certain embodiments of the present invention, semiconductornanocrystals that emit wavelengths characteristic of red light aredesirable. In certain embodiments, semiconductor nanocrystals capable ofemitting red light emit light having a peak center wavelength in a rangefrom about 615 nm to about 635 nm, and any wavelength in between whetheroverlapping or not, are preferred. For example, the semiconductornanocrystals can be capable of emitting red light having a peak centerwavelength of about 630 nm, of about 625 nm, of about 620 nm, or about615 nm. In certain embodiments, semiconductor nanocrystals capable ofemitting red light emit light having a peak center wavelength in a rangefrom about 600 nm to about 615 nm, and any wavelength in between whetheroverlapping or not, are preferred. For example, the semiconductornanocrystals can be capable of emitting red light having a peak centerwavelength of about 615 nm, of about 610 nm, of about 605 nm, or ofabout 600 nm.

In certain embodiments of the present invention, semiconductornanocrystals that emit wavelength characteristic of green light aredesirable. In certain preferred embodiments, semiconductor nanocrystalscapable of emitting green light emit light having a peak centerwavelength in a range from about 520 nm to about 545 nm, and anywavelength in between whether overlapping or not. For example, thesemiconductor nanocrystals can be capable of emitting green light havinga peak center wavelength of about 520 nm, of about 525 nm, of about 535nm, or of about 540 nm.

According to further aspects of the present invention, light-emittingsemiconductor nanocrystals exhibit a narrow emission profile less thanor equal to about 60 nm at full width half maximum (FWHM). In certainembodiments, the FWHM is less than about 60 nm, less than about 50 nm,less than about 40 nm, less than about 30 nm, or less than about 20 nm.In certain embodiments, a FWHM in a range from about 15 nm to about 60nm can be preferred. The narrow emission profile of semiconductornanocrystals of the present invention allows the tuning of thesemiconductor nanocrystals and mixtures of semiconductor nanocrystals toemit saturated colors thereby increasing color gamut and powerefficiency beyond that of conventional LED lighting displays.

A semiconductor nanocrystal described herein can be included in apopulation of semiconductor nanocrystals, a formulation or othercomposition, and/or end-use applications that includes othersemiconductor nanocrystals. One or more of such other semiconductornanocrystals can also comprise semiconductor nanocrystals describedherein. In such embodiments, one or more of the semiconductornanocrystals so included can be selected to have emissioncharacteristics that are distinct from those of any one or more of othernanocrystals.

For example, a population of semiconductor nanocrystals designed to emita predominant wavelength of, for example, in the green spectral regionand having an emission profile with a FWHM of about, for example, lessthan 40 nm can be included or used in combination with semiconductornanocrystals designed to emit a predominant wavelength in the redspectral region and having an emission profile with a FWHM of about, forexample 30-40 nm. Such combinations can be stimulated by blue light tocreate trichromatic white light.

The semiconductor nanocrystals used in a formulation, optical material,or other composition are selected based on the desired peak emissionwavelength or combinations of wavelengths desired for the particularintended end-use application for the formulation, optical material, orother composition.

In accordance with another aspect of the present invention, there isprovided a composition comprising a plurality of semiconductornanocrystals wherein the solid state photoluminescence efficiency of thecomposition at a temperature of 90° C. or above is at least 95% of thesolid state photoluminescence efficiency of the composition at 25° C.

In certain embodiments, the composition has a solid statephotoluminescence efficiency at the temperature of 90° C. or above thatis from 95 to 100% of the solid state photoluminescence efficiency at25° C.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the composition has a solid statephotoluminescence efficiency at the temperature of 90° C. or above thatis from 95 to 100% of the solid state photoluminescence efficiency at25° C.

In accordance with another aspect of the present invention, there isprovided a composition comprising a host material and a plurality ofsemiconductor nanocrystals wherein the solid state photoluminescenceefficiency of the composition is at least 80% at a temperature of 90° C.or above.

In certain embodiments, the temperature of 90° C. or above is in arange, for example, but not limited to, from 90° C. to about 200° C.,90° C. to about 180° C., 90° C. to about 160° C., 90° C. to about 140°C., 90° C. to about 120° C., or 90° C. to about 100° C.

In certain embodiments, the temperature of 90° C. or above is at atemperature, for example, but not limited to, of 100° C. or above, of120° C. or above, or of 140° C. or above.

In certain embodiments, the composition has a solid statephotoluminescence external quantum efficiency of at least 85% at atemperature of 90° C. or above.

In certain embodiments, the composition has a solid statephotoluminescence external quantum efficiency of at least 90% at atemperature of 90° C. or above.

In certain embodiments, the composition has a solid statephotoluminescence external quantum efficiency of at least 95% at atemperature of 90° C. or above.

In certain embodiments, the composition has a solid statephotoluminescence external quantum efficiency that is from 95 to 100% ata temperature of 90° C. or above.

In certain embodiments of the various aspects of the compositiondescribed herein, the composition preferably includes a semiconductornanocrystal described herein.

Examples of compositions include, but are not limited to, opticalmaterials, color converting materials, inks, paints, taggants,light-emitting materials, etc.

In certain embodiments of the various aspects of the compositiondescribed herein, the composition further includes a host material. Incertain of such embodiments, the semiconductor nanocrystals aredistributed within the host material. In certain of such embodiments, auniform or substantially uniform distribution of semiconductornanocrystals within the host material is preferred.

A host material can be selected based upon the intended end-useapplication for the composition. According to one aspect, a hostmaterial can comprise a flowable host material. Flowable host materialscan be useful for applications in which a composition is to be included,for example, in an optical component such as light transmissive glasstubes or capillary tubes or other glass containers, which are to beexposed to light. Such compositions can include various amounts of oneor more type of semiconductor nanocrystals and one or more hostmaterials. Such compositions can further include one or more scatterers.Other optional additives or ingredients can also be included in acomposition. In certain embodiments, a composition can further includeone or more initiators, e.g., without limitation, photo initiators. Oneof skill in the art will readily recognize from the present inventionthat additional ingredients can be included depending upon theparticular intended application for the semiconductor nanocrystals.

An optical material, color converting material, light-emitting material,or other composition within the scope of the disclosure may include ahost material, which may be present in an amount from about 50 weightpercent and about 99.5 weight percent, and any weight percent in betweenwhether overlapping or not. In certain embodiment, a host material maybe present in an amount from about 80 to about 99.5 weight percent.Examples of specific useful host materials include, but are not limitedto, polymers, oligomers, monomers, resins, binders, glasses, metaloxides, and other nonpolymeric materials. Preferred host materialsinclude polymeric and non-polymeric materials that are at leastpartially transparent, and preferably fully transparent, to preselectedwavelengths of light. In certain embodiments, the preselectedwavelengths can include wavelengths of light in the visible (e.g.,400-700 nm) region of the electromagnetic spectrum. Preferred hostmaterials include cross-linked polymers and solvent-cast polymers.Examples of other preferred host materials include, but are not limitedto, glass or a transparent resin. In particular, a resin such as anon-curable resin, heat-curable resin, or photocurable resin is suitablyused from the viewpoint of processability. Specific examples of such aresin, in the form of either an oligomer or a polymer, include, but arenot limited to, a melamine resin, a phenol resin, an alkyl resin, anepoxy resin, a polyurethane resin, a maleic resin, a polyamide resin,polymethyl methacrylate, polyacrylate, polycarbonate, polyvinyl alcohol,polyvinylpyrrolidone, hydroxyethylcellulose, carboxymethylcellulose,copolymers containing monomers or oligomers forming these resins, andthe like. Other suitable host materials can be identified by persons ofordinary skill in the relevant art.

Host materials can also comprise silicone materials. Suitable hostmaterials comprising silicone materials can be identified by persons ofordinary skill in the relevant art.

In certain embodiments and aspects of the inventions contemplated bythis disclosure, a host material comprises a photocurable resin. Aphotocurable resin may be a preferred host material in certainembodiments, e.g., in embodiments in which the composition is to bepatterned. As a photocurable resin, a photo-polymerizable resin such asan acrylic acid or methacrylic acid based resin containing a reactivevinyl group; a photo-crosslinkable resin which generally contains aphoto-sensitizer, such as polyvinyl cinnamate, benzophenone, or the likemay be used. A heat-curable resin may be used when a photo-sensitizer isnot used, or in combination. These resins may be used individually or incombination of two or more.

In certain embodiments and aspects of the inventions contemplated bythis disclosure, a host material can comprise a solvent-cast resin. Apolymer such as a polyurethane resin, a maleic resin, a polyamide resin,polymethyl methacrylate, polyacrylate, polycarbonate, polyvinyl alcohol,polyvinylpyrrolidone, hydroxyethylcellulose, carboxymethylcellulose,copolymers containing monomers or oligomers forming these resins, andthe like can be dissolved in solvents known to those skilled in the art.Upon evaporation of the solvent, the resin forms a solid host materialfor the semiconductor nanoparticles.

In certain embodiments, acrylate monomers and/or acrylate oligomerswhich are commercially available from Radcure and Sartomer can bepreferred.

Embodiments of the invention include compositions wherein the hostmaterial comprises a material with moderate or high dielectric orinsulating properties.

Embodiments of the invention include compositions wherein the hostmaterial comprises a material with electrically insulating properties.

Embodiments of the invention include compositions in which semiconductornanocrystals can be further encapsulated. Nonlimiting examples ofencapsulation materials, related methods, and other information that maybe useful are described in International Application No.PCT/US2009/01372 of Linton, filed 4 Mar. 2009 entitled “ParticlesIncluding Nanoparticles, Uses Thereof, And Methods” and U.S. PatentApplication No. 61/240,932 of Nick et al., filed 9 Sep. 2009 entitled“Particles Including Nanoparticles, Uses Thereof, And Methods”, each ofthe foregoing being hereby incorporated herein by reference in itsentirety.

The total amount of semiconductor nanocrystals included in an opticalmaterial, color converting material, light emitting material, or othercomposition that includes a host material, such as for example apolymer, within the scope of the invention can be in a range from about0.01 to about 50 weight percent, and any weight percent in between. Incertain applications, an amount in a range from about 0.05 weightpercent to about 5 weight percent can be desirable. In certainapplications, an amount in a range from about 0.01 weight percent toabout 10 weight percent can be desirable. Higher loadings may bedesirable to achieve thinner films with high OD, and hence lower thermalresistance. The amount of semiconductor nanocrystals included in anoptical material or other composition can vary within such rangedepending upon the application and the form in which the semiconductornanocrystals are included (e.g., film, optics (e.g., capillary),encapsulated film, etc.), which can be chosen based on the particularend application.

In certain embodiments of the various aspects of the compositiondescribed herein, the composition further includes scatterers.

Scatterers, also referred to as scattering agents, within the scope ofthe disclosure may be present, for example, in an amount of betweenabout 0.01 weight percent and about 1 weight percent. Amounts ofscatterers outside such range may also be useful. Examples of lightscatterers (also referred to herein as scatterers or light scatteringparticles) that can be used in the embodiments and aspects of theinventions described herein, include, without limitation, metal or metaloxide particles, air bubbles, and glass and polymeric beads (solid orhollow). Other light scatterers can be readily identified by those ofordinary skill in the art. In certain embodiments, scatterers have aspherical shape. Preferred examples of scattering particles include, butare not limited to, TiO₂, SiO₂, BaTiO₃, BaSO₄, and ZnO. Particles ofother materials that are non-reactive with the host material and thatcan increase the absorption pathlength of the excitation light in thehost material can be used. In certain embodiments, light scatterers mayhave a high index of refraction (e.g., TiO₂, BaSO₄, etc) or a low indexof refraction (gas bubbles).

Selection of the size and size distribution of the scatterers is readilydeterminable by those of ordinary skill in the relevant art. The sizeand size distribution can be based upon the refractive index mismatch ofthe scattering particle and the host material in which the lightscatterers are to be dispersed, and the preselected wavelength(s) to bescattered according to light scattering theory, e.g., Rayleigh or Miescattering theory. The surface of the scattering particle may further betreated to improve dispersibility and stability in the host material.Such surface treatments can be organic or inorganic, e.g. silica coatingon a titania particle, such as available for purchase at Evonik. In oneembodiment, the scattering particle comprises TiO₂ (R902+ from DuPont)having a 0.405 μm median particle size in a concentration in a rangefrom about 0.01 to about 1% by weight.

The amount of scatterers in a formulation is useful in applicationswhere the formulation which may be in the form of an ink is contained ina clear vessel having edges to limit losses due the total internalreflection. The amount of the scatterers may be altered relative to theamount of semiconductor nanocrystals used in the formulation. Forexample, when the amount of the scatter is increased, the amount ofsemiconductor nanocrystals may be decreased.

Other optional additives or ingredients can also be included in acomposition. In certain embodiments, a composition can further includeone or more photo initiators. In certain embodiments, a composition canfurther include one or more cross-linking agents. In certainembodiments, a composition can further include one or more thixotropes.One of skill in the art will readily recognize from the presentinvention that additional additives or ingredients at suitable amountscan be selected from known or commercially available additives andingredients and included within a formulation depending upon theparticular intended application for the semiconductor nanocrystals andcomposition.

The present invention includes compositions including one or moresemiconductor nanocrystals described herein and other products includingone or more semiconductor nanocrystals described herein. Examples ofsuch compositions and/or products include, but are not limited to, lightemitting materials, color-converting materials, optical materials, inks,paints, taggants, optical components, backlighting units, displays,electronic devices, opto-electronic devices, light-emitting devices,color-converting materials, lamps, light bulbs, luminaires, etc. Incertain embodiments of such compositions, the one or more semiconductornanocrystals can be a constituent of a composition, that may include oneor more other ingredients. In certain embodiments of such otherproducts, the one or more semiconductor nanocrystals can be included ina composition included in the other product and/or included in acomponent part of the other product.

Embodiments of the invention include a light emitting device including alight emitting material comprising at least one semiconductornanocrystal described herein.

Embodiments of the invention include a light emitting device comprisingan inorganic semiconductor light emitting diode wherein at least onesemiconductor nanocrystal described herein is arranged to receive andconvert at least a portion of light emitted by the light-emitting diodefrom a first emission wavelength to one or more predeterminedwavelengths. One or more of such light-emitting devices can be furtherincluded in a lighting fixture or system. In further embodiments, alight emitting device can include a different type of light source inlieu of an inorganic semiconductor light emitting diode.

Embodiments of the invention also include a light-emitting devicecomprising a light-emitting element and an optical material including atleast one semiconductor nanocrystal described herein arranged to receiveand convert at least a portion of light emitted by the light emittingelement from a first emission wavelength to one or more predeterminedwavelengths, wherein the optical material comprises a composition taughtherein.

In certain embodiments, the optical material can encapsulate at leastthe light emitting-surface of the light-emitting element. In certainembodiments, the optical material can be spaced from the lightemitting-surface of the light-emitting element. In certain of suchembodiments, the optical material can be included in the light-emittingdevice in the form of an optical component.

Embodiments of the invention also include display including a backlightmember including a plurality of light-emitting diodes and an opticalmaterial arranged to receive and convert at least a portion of lightemitted by at least a portion of the light-emitting diodes from a firstemission wavelength to one or more predetermined wavelengths, whereinthe optical material comprises a composition taught herein.

In certain embodiments, the display comprises a liquid crystal display.

In accordance with another aspect of the present invention, there isprovided a method for preparing semiconductor nanocrystals comprising:introducing one or more first shell chalcogenide precursors and one ormore first shell metal precursors to a reaction mixture includingsemiconductor nanocrystal cores, wherein the first shell chalcogenideprecursors are added in an amount greater than the first shell metalprecursors by a factor of at least about 2 molar equivalents andreacting the first shell precursors at a first reaction temperature ofat least 300° C. to form a first shell on the semiconductor nanocrystalcores.

In certain preferred embodiments, the first shell chalcogenideprecursors are added in an amount greater than the first shell metalprecursors by a factor from about 2 to about 8 molar equivalents.

In certain embodiments, a first shell chalcogenide precursor comprisesan alkanethiol precursor. Examples of alkanethiol precursors include,but are not limited to, octanethiol, dodecanethiol, hexadecanethiol,etc. In certain embodiments, dodecanethiol can be a preferred sulfurprecursor.

Examples of other chalcogenide precursors include, but are not limitedto, trialkyl phosphine selenides such as (tri-n-octylphosphine) selenide(TOPSe) or (tri-n-butylphosphine) selenide (TBPSe), dialkyl phosphineselenides such as di-iso-butylphosphine-selenide (DiBPSe),bis(trimethylsilyl) selenide ((TMS)₂Se), octadecene-Se, trialkylphosphine tellurides such as (tri-n-octylphosphine) telluride (TOPTe);dialkyl phosphine tellurides such as di-iso-butylphosphine telluride(DiBPTe), hexapropylphosphorustriamide telluride (HPPTTe),bis(trimethylsilyl)telluride ((TMS)₂Te), octadecene-Te.

In certain embodiments, a first shell metal precursor comprises a metalcarboxylate.

A preferred example includes zinc oleate (Zn(Oleate)₂).

In certain preferred embodiments, the first reaction temperature is from300° C. to 360° C.

In certain of such embodiments, the first shell is applied at atemperature in excess of 300° C. for a time of 2 minutes up to 30minutes. Times may be varied outside of this range, depending upon theparticular precursors.

Semiconductor nanocrystal cores preferably comprise an inorganicsemiconductor material.

Examples of semiconductor materials that can be included in asemiconductor nanocrystal core include, but are not limited to, a GroupIV element, a Group II-VI compound, a Group II-V compound, a GroupIII-VI compound, a Group III-V compound, a Group IV-VI compound, a Groupcompound, a Group II-IV-VI compound, a Group II-IV-V compound, an alloyincluding any of the foregoing, and/or a mixture including any of theforegoing, including ternary and quaternary mixtures or alloys. Anon-limiting list of examples include ZnO, ZnS, ZnSe, ZnTe, CdO, CdS,CdSe, CdTe, MgS, MgSe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe,InAs, InN, InP, InSb, AlAs, AlN, AlP, AlSb, TlN, TlP, TlAs, TlSb, PbO,PbS, PbSe, PbTe, Ge, Si, an alloy including any of the foregoing, and/ora mixture including any of the foregoing, including ternary andquaternary mixtures or alloys.

In certain preferred embodiments, semiconductor nanocrystal corescomprise cadmium selenide.

In certain embodiments, the first shell comprises a first semiconductormaterial and has a thickness greater than or equal to the thickness of 1monolayer of the first semiconductor material.

In certain embodiments, the first shell comprises a first semiconductormaterial and has a thickness up to the thickness of about 10 monolayersof the first semiconductor material.

In certain preferred embodiments, the semiconductor nanocrystal core isprepared in accordance with the method described in U.S. PatentApplication No. 61/562,465, filed 22 Nov. 2011, of Liu, et al., for“Method Of Making Quantum Dots”, which is hereby incorporated herein byreference in its entirety.

In certain of such preferred embodiments, the method further includes afirst step for preparing semiconductor cores, the first step comprisingcombining one or more highly reactive first chalcogenide precursors, oneor more highly reactive first metal precursors, and a seed stabilizingagent at a reaction temperature to form a reaction mixture where theratio of metal to chalcogenide is in a range from 1 to 0.5 to 1 to 1,quenching the reaction mixture resulting in semiconductor nanocrystalcores. In certain of such embodiments, a first highly reactivechalcogenide precursor comprises secondary phosphine chalcogenideprecursor and a first highly reactive metal precursor comprises a metalcarboxylate. In certain embodiments, cadmium oleate (Cd(Oleate)₂) ispreferred. In certain embodiments, the seed stabilizing agent comprisesa phosphonic acid. In certain embodiments, octadecylphosphonic acid ispreferred. The reaction temperature for forming the cores is preferablysufficient for forming the semiconductor nanocrystal cores. For example,a preferred reaction temperature for preparing a semiconductornanocrystal core comprising CdSe is about 270° C. Preferably, when thereaction is quenched, there are no unreacted first metal precursors orfirst phosphine chalcogenide precursor in the reaction mixture includingthe cores.

Most preferably, the cores are stable with respect to maintaining itsabsorbance peak Half Width at Half Maximum (HWHM), and peak position towithin 5 nm of its starting wavelength upon heating up to hightemperature (250° C.-320° C.) for a period of up to 30 minutes.

The method can further comprise introducing one or more second shellchalcogenide precursors and one or more second shell metal precursors tothe reaction mixture including semiconductor nanocrystal cores includingthe first shell at a second reaction temperature of at least 300° C.,wherein the second shell chalcogenide precursors are added in an amountof at least 0.7 molar equivalents of the second shell metal precursors,and reacting the second shell precursors to form a second shell over thefirst shell on the semiconductor nanocrystal cores.

In certain preferred embodiments, the second shell chalcogenideprecursors are added in an amount of 0.7 to 10 molar equivalents of thesecond shell metal precursors. Amounts outside of this range can beused, depending on the nature of the particular precursor used.

In certain embodiments, a second shell chalcogenide precursor comprisesan alkanethiol precursor. Examples of alkanethiol precursors include,but are not limited to, octanethiol, dodecanethiol, hexadecanethiol,etc. In certain embodiments, dodecanethiol can be a preferred sulfurprecursor.

Examples of other chalcogenide precursors include, but are not limitedto, trialkyl phosphine selenides such as (tri-n-octylphosphine) selenide(TOPSe) or (tri-n-butylphosphine) selenide (TBPSe), dialkyl phosphineselenides such as di-iso-butylphosphine-selenide (DiBPSe),bis(trimethylsilyl) selenide ((TMS)₂Se), octadecene-Se, trialkylphosphine tellurides such as (tri-n-octylphosphine) telluride (TOPTe);dialkyl phosphine tellurides such as di-iso-butylphosphine telluride(DiBPTe), hexapropylphosphorustriamide telluride (HPPTTe),bis(trimethylsilyl)telluride ((TMS)₂Te), octadecene-Te.

In certain embodiments, a second shell metal precursor comprises a metalcarboxylate. Preferred examples include, but are not limited to, zincoleate (Zn(Oleate)₂) and/or cadmium oleate (Cd(Oleate)₂).

In certain preferred embodiments, the second reaction temperature ispreferably at least 315° C. In certain embodiments, the second reactiontemperature can be in a range from 315° C. to 360° C. Temperature may bevaried outside of this range, depending upon the particular precursors.

In certain more preferred embodiments, the second shell is formed bycontrolled addition of second shell precursors over a period from 10minutes up to 2 hours. Times may be varied outside of this range,depending upon the particular precursors.

In certain embodiments, the second shell comprises a secondsemiconductor material and has a thickness greater than or equal to thethickness of 3 monolayers of the second semiconductor material.

In certain embodiments, the second shell has a thickness up to thethickness of about 20 monolayers of the second semiconductor material.

In certain embodiments, the first shell comprises zinc sulfide, and thesecond shell comprises one or more metals wherein the one or metalscomprises from 0 to less than 100% cadmium.

In certain embodiments, the core comprises CdSe, the first shellcomprises ZnS at a thickness of about 3-4 monolayers of ZnS, and thesecond shell comprises Cd_(1-x)Zn_(x)S wherein 0<x≤1 at a thickness ofabout 9-10 monolayers of Cd_(1-x)Zn_(x)S.

In an example of a preferred embodiment of a semiconductor nanocrystalwith peak emission at a wavelength in a range from 600 nm to 635 nm, thefirst shall can comprise a thickness of about 3.66 monolayers of thematerial constituting the first shell and the second shell can have athickness of about 9.5 monolayers of the material constituting thesecond shell.

In certain preferred embodiments of the methods described herein, thesemiconductor nanocrystal core and shells are undoped.

In accordance with another aspect of the present invention, there isprovided a population of semiconductor nanocrystals prepared inaccordance with a method described herein.

In accordance with another aspect of the present invention, there isprovided a population of overcoated semiconductor nanocrystals preparedin accordance with a method described herein.

The present invention also includes compositions including one or moresemiconductor nanocrystals prepared by any of the methods describedherein and other products including one or more semiconductornanocrystals described herein. Examples of such compositions and/orproducts include, but are not limited to, light emitting materials,color-converting materials, inks, paints, taggants, optical components,backlighting units, displays, electronic devices, opto-electronicdevices, light-emitting devices, color-converting materials, lamps,light bulbs, luminaires, etc. In certain embodiments of suchcompositions, the one or more semiconductor nanocrystals can be aconstituent of a composition, that may include one or more otheringredients. In certain embodiments of such other products, the one ormore semiconductor nanocrystals can be included in a compositionincluded in the other product and/or included in a component part of theother product.

Embodiments of the invention include a light emitting device including alight emitting material comprising at least one semiconductornanocrystal prepared by any of the methods described herein.

Embodiments of the invention include a light emitting device comprisingan inorganic semiconductor light emitting diode wherein at least onesemiconductor nanocrystal prepared by any of the methods describedherein is arranged to receive and convert at least a portion of lightemitted by the light-emitting diode from a first emission wavelength toone or more predetermined wavelengths. One or more of suchlight-emitting devices can be further included in a lighting fixture orsystem. In further embodiments, a light emitting device can include adifferent type of light source in lieu of an inorganic semiconductorlight emitting diode.

Embodiments of the invention also include a light-emitting devicecomprising a light-emitting element and an optical material including atleast one semiconductor nanocrystal prepared by any of the methodsdescribed herein arranged to receive and convert at least a portion oflight emitted by the light emitting element from a first emissionwavelength to one or more predetermined wavelengths, wherein the opticalmaterial comprises a composition taught herein.

In certain embodiments, the optical material can encapsulate at leastthe light emitting-surface of the light-emitting element. In certainembodiments, the optical material can be spaced from the lightemitting-surface of the light-emitting element. In certain of suchembodiments, the optical material can be included in the light-emittingdevice in the form of an optical component.

Embodiments of the invention also include display including a backlightmember including a plurality of light-emitting diodes and an opticalmaterial arranged to receive and convert at least a portion of lightemitted by at least a portion of the light-emitting diodes from a firstemission wavelength to one or more predetermined wavelengths, whereinthe optical material comprises a composition taught herein.

In certain embodiments, the display comprises a liquid crystal display.

In accordance with another aspect of the present invention, there isprovided a color-converting material comprising a semiconductornanocrystal prepared in accordance with a method described herein.

In accordance with another aspect of the present invention, there isprovided a lamp comprising a semiconductor nanocrystal prepared inaccordance with a method described herein.

In accordance with another aspect of the present invention, there isprovided a light bulb including a semiconductor nanocrystal prepared inaccordance with a method described herein.

In accordance with another aspect of the present invention, there isprovided a luminaire including a semiconductor nanocrystal prepared inaccordance with a method described herein.

The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.

EXAMPLES Example 1

Following is an example of a preferred embodiment of a method inaccordance with the present invention:

Example 1A Semiconductor Nanocrystals Capable of Emitting Red Light

Synthesis of CdSe Cores:

The following are added to a 1 L glass reaction vessel:trioctylphosphine oxide (17.10 g), 1-octadecene (181.3 g),1-octadecylphosphonic acid (2.09, 24.95 mmol), and Cd(Oleate)₂ (1 Msolution in trioctylphosphine, 24.95 mL, 24.95 mmol). The vessel issubjected to 3 cycles of vacuum/nitrogen at 120° C., and the temperatureis raised to 270° C. under nitrogen. At 270° C., a solution of 1 Mdiisobutylphosphine selenide in N-dodecylpyrrolidone (DIBP-Se, 19.46 mL,19.46 mmol) is rapidly injected, within a period of less than 1 second,followed by injection of 1-octadecene (76.6 mL) to rapidly drop thetemperature to about 240° C. resulting in the production of quantum dotswith an initial absorbance peak between 420-450 nm. 5-20 seconds afterthe ODE quench, a solution of Cd(Oleate)₂ (0.5 M in a 50/50 v/v mixtureof TOP and ODE) is continuously introduced along with a solution ofDIBP-Se (0.4 M in a 60/40 v/v mixture of N-dodecylpyrrolidone and ODE)at a rate of 61.7 mL/hr. At 15 min, the infusion rate is increased to123.4 mL/hr. At 25 min, the infusion rate is increased to 185.2 mL/hour.At 35 min, the infusion rate is increased to 246.9 mL/hr. At 45 min, theinfusion rate is increased to 329.2 mL/hr. A total of 136.8 mL of eachprecursor is delivered while the temperature of the reactor ismaintained between 215-240° C. At the end of the infusion, the reactionvessel is cooled using room temperature airflow over a period of 5-15min. The final material is used as is without further purification(First absorbance peak: 559 nm, Total volume: 587 mL, Reaction yield:99%). The absorption spectrum of the core is shown in FIG. 5A.

Synthesis of CdSe/ZnS/CdZnS Core/Shell/Shell:

CdSe cores synthesized as described in the preceding paragraph, with afirst absorbance peak of 559 nm (72.9 mL, 8 mmol Cd), are mixed withZn(Oleate)₂ (44.0 mL, 0.5 M in TOP) and 1-octadecene (84.1 mL). Thesolution is heated to 320° C., upon which a syringe containing1-dodecanethiol (39.54 mL) is swiftly injected. After 2 min, when thetemperature recovers to 310-315° C., the overcoat precursors aredelivered via a syringe pump over a period of 30 min. The twoovercoating precursor stocks include the following: 1) Zn(Oleate)₂(53.87 mL, 0.5 M in TOP) mixed with Cd(Oleate)₂ (64.64 mL, 1.0 M inTOP), and 2) dodecanethiol (33.69 mL) mixed with 1-octadecene (67.86 mL)and TOP (16.96 mL). During the overcoating precursor infusion, thetemperature is kept between 320° C.-330° C. Any volatiles from thesystem are allowed to distill over and leave the system in order for thetemperature to reach 320-330 C. After the infusion ends, the sample isannealed for 5 min at 320-330° C. and cooled to room temperature over aperiod of 5-15 min. The final core/shell material is precipitated viathe addition of butanol and methanol at a 2:1 ratio v/v. The pellet isisolated via centrifugation, and redispersed into toluene (10 mL) forstorage (Emission 598 nm, FWHM 24 nm, Film EQE at RT: 99%, Film EQE at140° C.: 90-94%). The absorption and emission spectrum are shown in FIG.6A.

Example 1B Semiconductor Nanocrystals Capable of Emitting Green Light

Synthesis of CdSe Cores (448 nm Target):

The following are added to a 1 L steel reaction vessel:trioctylphosphine oxide (51.88 g), 1-octadecene (168.46 g),1-octadecylphosphonic acid (33.09 g, 98.92 mmol), and Cd(Oleate)₂ (1Msolution in trioctylphosphine, 98.92 mL, 98.92 mmol). The vessel issubjected to 3 cycles of vacuum/nitrogen at 120° C., and the temperatureis raised to 270° C. under nitrogen. At 270° C., a solution of 1Mdiisobutylphosphine selenide in N-dodecylpyrrolidone (DIBP-Se, 77.16 mL,77.16 mmol) is rapidly injected, within a period of less than 1 second,followed by injection of 1-octadecene (63.5 mL) to rapidly drop thetemperature to about 240° C. resulting in the production of quantum dotswith an initial absorbance peak between 420-430 nm. 5-20 seconds afterthe ODE injection, a solution of Cd(Oleate)₂ (0.5 M in a 50/50 v/vmixture of TOP and ODE) is continuously introduced along with a solutionof DIBP-Se (0.4 M in a 60/40 v/v mixture of N-dodecylpyrrolidone andODE) at a rate of 29.0 mL/min. A total of 74.25 mL of each precursor isdelivered while the temperature of the reactor is maintained between205-240° C. At the end of the infusion, the reaction vessel is cooledrapidly by immersing the reactor in a squalane bath chilled with liquidnitrogen to rapidly bring the temperature down to <150° C. (within 2minutes). The final material is used as is without further purification(First absorbance peak: 448 nm, Total volume: 702 mL, Reaction yield:99%). The absorption spectrum of the core is shown in FIG. 5B.

Synthesis of CdSe/ZnS/CdZnS Core/Shell/Shell

CdSe cores synthesized as described in the preceding paragraph, with afirst absorbance peak of 448 nm (47.61 mL, 7.74 mmol Cd), are mixed withdodecanethiol (30.67 mL) in a syringe. A reaction flask containingZn(Oleate)₂ (128.0 mL, 0.5 M in TOP) is heated to 300° C., upon whichthe syringe containing cores and 1-dodecanethiol is swiftly injected.When the temperature recovers to 310° C. (between 2-8 min), the overcoatprecursors are delivered via a syringe pump over a period of 32 min. Thetwo overcoating precursor stocks include the following: 1) Zn(Oleate)₂(155.59 mL, 0.5M in TOP) mixed with Cd(Oleate)₂ (51.86 mL, 1.0 M inTOP), and 2) dodecanethiol (21.74 mL) mixed 1-octadecene (19.75 mL).During the overcoating precursor infusion, the temperature is keptbetween 320-330° C. Any volatiles from the system are allowed to distillover and leave the system in order for the temperature to reach 320-330°C. After the infusion ends, the sample is annealed for 3 min at 320-330°C. and cooled to room temperature over a period of 5-15 min. The finalcore/shell material is precipitated via the addition of butanol andmethanol at a 2:1 ratio v/v. The pellet is isolated via centrifugation,and redispersed into toluene for storage (Emission 517 nm, FWHM 40 nm,Film EQE at RT: 99%, Film EQE at 140° C.: 85-90%). Absorption andemission spectrum is shown in FIG. 6B.

Example 2 Control Sample (Red) Preparation of Semiconductor NanocrystalsCapable of Emitting Red Light with3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid

Synthesis of CdSe Cores:

45.94 mmol cadmium acetate is dissolved in 669.55 mmol oftri-n-octylphosphine at 100° C. in a 250 mL 3-neck round-bottom flaskand then dried and degassed for one hour. 814.69 mmol oftrioctylphosphine oxide and 104.85 mmol of octadecylphosphonic acid areadded to a 0.5 L stainless steel reactor and dried and degassed at 140°C. for one hour. After degassing, the Cd solution is added to thereactor containing the oxide/acid and the mixture is heated to 270° C.under nitrogen. Once the temperature reaches 270° C., 425 mmol ofaerated tri-n-butylphosphine (see preparation below) is injected intothe flask. The temperature of the mixture is then raised to 305° C.where 105 mL of 1.5 M aerated TBP-Se (see preparation below) is thenrapidly injected. The reaction is allowed to proceed for 8 minutes and45 seconds (aliquots taken at 1 minute intervals to observe the growthand corresponding absorption wavelength shift) at which point thereactor is then immediately submerged in partially frozen (via liquidnitrogen) squalane bath rapidly reducing the temperature of the reactionto below 100° C. The first absorption peak of the nanocrystals is 557nm. The CdSe cores are precipitated out of the growth solution inside anitrogen atmosphere glovebox by adding a 3:1 mixture of methanol andisopropanol. The isolated cores are then dissolved in hexane and used tomake core-shell materials.

Preparation of Aerated TBP-Se:

9.5 mol of TBP (Strem Lot A4329040) is loaded into a 3 L 3-neckround-bottom flask. A tank of dry compressed air is used to bubble dryair into the TBP at a rate of 4 L per minute (min). The temperature ofthe TBP is monitored during the aeration process.

Elapsed Time (min) Temperature (° C.) 0 22.8 14 30.7 58 43.1 80 47.1 10854.9 188 79.5

This aerated TBP is then combined with pure TBP (Strem 99%) in a ratioof 1:3 and then used as aerated TBP. The TBP-Se is made by mixing 105 mLof aerated TBP with 13.03 g of Se shot generating 1.5 M TBP-Se for usein the core preparation above.

Synthesis of Red Emitting CdSe/CdZnS Core-Shell Nanocrystals:

517.3 mmol of trioctylphosphine oxide and 48.3 mmol of3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid are loaded into a 0.5 Lglass reactor. The mixture is then dried and degassed in the reactor byheating to 120° C. for about an hour. The reactor is then cooled to 70°C. and the hexane solution containing isolated CdSe cores (3.96 mmol Cdcontent) is added to the reaction mixture. The hexane is removed underreduced pressure. Dimethyl cadmium, diethyl zinc, andhexamethyldisilathiane are used as the Cd, Zn, and S precursors,respectively. The Cd and Zn are mixed in equimolar ratios while the S isin two-fold excess relative to the Cd and Zn. The Cd/Zn (23.1 mmol and23.1 mmol respectively) and S (23.1 mmol) samples are each dissolved in40 mL of trioctylphosphine inside a nitrogen atmosphere glove box. Oncethe precursor solutions are prepared, the reaction flask is heated to155° C. under nitrogen. The precursor solutions are added dropwise tothe reactor at 155° C. at a rate of 20 mL per hour using a syringe pump.After the reaction proceeds for 1 hour, the precursor injection isstopped and the reaction temperature is allowed to return to roomtemperature. The nanocrystals are precipitated out of the growthsolution by transferring to a 3:1 mixture of methanol and isopropanoland then isolating in a nitrogen atmosphere glovebox. The isolatedcore-shell nanocrystals are then dissolved in toluene. Thespecifications are as follows: Emission=612 nm; FWHM=32 nm; QY=81% intoluene.

Example 3 Control Sample (Green) Preparation of SemiconductorNanocrystals Capable of Emitting Green Light

Synthesis of ZnSe Cores:

7.0 mmol diethyl zinc is dissolved in 50 mL of tri-n-octylphosphine andmixed with 10 mL of 1 M TBP-Se. 0.374 mol of Oleylamine is loaded into a250 mL 3-neck flask, dried and degassed at 90° C. for one hour. Afterdegassing, the flask is heated to 310° C. under nitrogen. Once thetemperature reaches 310° C., the Zn solution is injected and thereaction mixture is heated at 270° C. for 15-30 minutes while aliquotsof the solution are removed periodically in order to monitor the growthof the nanocrystals. Once the first absorption peak of the nanocrystalsreaches 350 nm, the reaction is stopped by dropping the flasktemperature to 160° C. and the ZnSe core materials are used withoutfurther purification for preparation of CdZnSe cores.

Synthesis of CdZnSe Cores:

22.4 mmol dimethylcadmium is dissolved in 80 mL of tri-n-octylphosphineand mixed with 24 mL of 1 M TBP-Se. In a 1 L glass reactor, 0.776 mol oftrioctylphosphine oxide and 42 mmol of octadecylphosphonic acid areloaded, dried and degassed at 120° C. for one hour. After degassing, theoxide/acid is heated to 160° C. under nitrogen and the entire ZnSe corereaction mixture (see above) is cannula transferred at 160° C. into the1 L reactor, immediately followed by the addition of Cd/Se solution overthe course of 20 minutes via syringe pump. The reaction mixture is thenheated at 150° C. for 16-20 hours while aliquots of the solution areremoved periodically in order to monitor the growth of the nanocrystals.The reaction is stopped by cooling the mixture to room temperature oncethe emission peak of the CdZnSe cores reaches 480 nm. The CdZnSe coresare precipitated out of the growth solution inside a nitrogen atmosphereglove box by adding a 2:1 mixture of methanol and n-butanol. Theisolated cores are then dissolved in hexane and used to make core-shellmaterials.

Synthesis of CdZnSe/CdZnS Core-Shell Nanocrystals:

0.72 mol of trioctylphosphine oxide and 70 mmol of3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid are loaded into a 1 Lglass reactor. The mixture is then dried and degassed in the reactor byheating to 120° C. for about an hour. The reactor is then cooled to 75°C. and the hexane solution containing isolated CdZnSe cores (2.74 mmolCd content) is added to the reaction mixture. The hexane is removedunder reduced pressure. Dimethyl cadmium, diethyl zinc, andhexamethyldisilathiane are used as the Cd, Zn, and S precursors,respectively. The Cd and Zn are mixed in a 3:10 ratio while the S isequimolar relative to Cd and Zn combined. The Cd/Zn (7.2/16.9 mmol ofdimethylcadmium and diethylzinc) and S (24.2 mmol ofhexamethyldisilathiane) samples are each dissolved in 40 mL oftrioctylphosphine inside a nitrogen atmosphere glove box. Once theprecursor solutions are prepared, the reactor is heated to 150° C. undernitrogen. The precursor solutions are added dropwise over the course of2 hours at 150° C. using a syringe pump. After the shell growth, thenanocrystals are transferred to a nitrogen atmosphere glovebox andprecipitated out of the growth solution by adding a 3:1 mixture ofmethanol and isopropanol. The isolated core-shell nanocrystals are thendissolved in hexane. The specifications are as follows: Emission=523 nm;FWHM=37 nm; QY=73% in toluene.

Example 4 Preparation of Ink Composition & Films

The following describes preparation of an ink formulation includingsemiconductor nanocrystals and preparation of a film from such inkformulation.

Example 4A Preparation of Ink Formulation

10 mg of semiconductor nanocrystals (inorganic mass as determined viathermal gravimetric analysis (TGA)) in toluene is added to 1 mL ofEbecyl 150 and degassed under reduced pressure to remove the toluene andoxygen. Once the toluene is removed, three purge and N₂ back-fill cyclesare completed and then 10 mg of TiO₂ is added to the formulation and themixture is degassed under reduced pressure while stirring in order todisperse the TiO₂. Once these steps are completed, 1 drop (˜12 mg) ofIrgacure 2022 is added to the formulation and the mixture is stirredunder air for a few minutes. The formulation is then ready for filmpreparation.

Example 4B Preparation of Film

A film prepared from an ink formulation prepared as generally describedin Example 4A is prepared as follows. ˜5-10 μL of the formulation isdropped onto a 15 mm diameter borosilicate glass disc (˜230+/−20 um inthickness). A second 15 mm disk is set on top of the drop of formulationsandwiching the ink between the glass slides. Care is taken to minimizethe amount of ink at the edges that is not completely sandwiched by theglass slides. The sandwich is then brought into a N₂ purge box andinserted into a UV curing station (Dymax 5000-EC Series UV Curing FloodLamp System) and cured with the following curing conditions: Dymax MetalHalide “D” Bulb; Part #38560; 80-100 milliWatts (mW)/square centimeter(cm²) excitation power with a cure time of 10 seconds. Once the film iscured, the films are then irradiated with 25 mW/cm² of 450 nm LED lightwhile on a hot plate set at 50° C. for 12-18 hrs. (Alternatively, thesamples can be irradiated with approximately 100 mW/cm² of 450 nm LEDlight while on a hot plate set at 80° C. for 1 hour). After thisprocess, the EQE of the film is measured in a QEMS (Labsphere product)integrating sphere system. The films are then ready for temperaturedependent efficiency measurements.

Solid state photoluminescence external quantum efficiency (also referredto herein as “EQE” or “solid state photoluminescence efficiency) can bemeasured in an integrating sphere using a NIST traceable calibratedlight source, using a method such as that developed by Mello et al.,Advanced Materials 9(3):230 (1997), which is hereby incorporated byreference. Such measurements can also be made with a QEMS from LabSphere(which utilizes a 4 in sphere; e.g. QEMS-2000: World Wide Websitelaser2000.nl/upload/documenten/fop_21-en2.pdf).

Example 4C PL vs. Temperature Measurement Protocol

With the room temperature (25° C.) EQE measured in an integrating sphere(Example 4B), the sample is then measured on a hotplate at roomtemperature. The measurement involves optically exciting the sample at awavelength shorter than the band edge absorption of the QDs (i.e. 1^(st)excitonic absorption feature) and collecting both a portion of the PLemission from the sample as well as a portion of the excitation lightafter it interacts with the sample (this light is proportional to theabsorption of the sample). The sample temperature is then raised via thehotplate and equilibrated at an elevated temperature for ˜1 min (thetemperature should not rise slower than 10° C./min) and the sample isthen measured again. This process is repeated for multiple temperaturesbetween 25° C. and about 140° C. or above. Measurements can be atpreselected temperature intervals, e.g., at every 5, 10, or 20 degreeintervals. Other intervals can be selected. The samples are heated andthe measurements taken in the absence of oxygen. For each data point,the sample is held at a given temperature for about <˜1-2 minutes whenPL is measured. The EQE measurements were made using a 440 nm laserlight source. Other adequate light sources include 405 nm laser or blue(405 and 440-450 nm) LED light sources. Monochromatic light from a whitelight monochromator can also be used. The light source should excite thesample with a flux/power density no greater than 100 mW/cm². Preferably,the excitation power density used to measure the sample is lower thanthat used to expose the sample prior to room temperature EQE measurement(as described in preparation of the film, Example 4B). The optical pathof the system (both excitation light and emitted semiconductornanocrystal light) is not altered during data collection.

Example 5

The EQE data presented in Table 1 and related figures are calculatedbased on the integrated PL change with temperature and correlated backto the room temperature (RT) EQE for the film. The integrated PL at RTis set equal to the RT measured EQE and therefore any change in PL isthen an equivalent % change in EQE with adjustment for any absorptionchange at elevated temperatures.

The measurements used to calculate the values in Table 1 and the relatedfigures are based on sample films prepared with the semiconductornanocrystals of the invention (the film being prepared as generallydescribed in Example 4 with nanocrystals prepared generally inaccordance with the procedure described in Examples 1A (red) and 1B(green)) and control films (a red control film and a green control filmprepared as generally described in Example 4 with semiconductornanocrystals prepared generally in accordance with the proceduredescribed in Example 2 (red) and Example 3 (green).

TABLE 1 EQE (%) at Temperature Temperature Sample 25° C. 90° C. 140° C.Control (Red) 81 75 Control (Green) 81 68 Improved (Red) 95 95 91Improved (Green) 99 97 88

FIGS. 1A and 1B graphically depicts the calculated EQE values from Table1 as a function of temperature.

As graphically shown in FIGS. 1A and 1B, the calculated EQE values forthe semiconductor nanocrystal of the present invention, as preferablyprepared in accordance with a method of the present invention are atleast 10% higher at room temperature (e.g., 20° C.-25° C.) than thecontrol (semiconductor nanocrystals of Examples 2 and 3), with thedifference being greater with increasing temperature. While not wishingto be bound by theory, this illustrates a reduction in the quenching ofsemiconductor nanocrystal emission as a function of temperature (alsoreferred to as “thermal quenching”.)

This result is further illustrated for the same samples in FIGS. 2A and2B as a normalized integrated plot of PL versus temperature forsemiconductor nanocrystals in accordance with the present invention, aspreferably prepared in accordance with a method of the presentinvention, compared to the control semiconductor nanocrystals ofExamples 2 and 3. FIGS. 2A and 2B show a % drop in PL vs. temperaturefor the comparative nanocrystals that is significantly greater than thedrop observed for the nanocrystals of the present invention.

For assessing the EQE vs. temperature response of a semiconductornanocrystal sample, a relative EQE measurement can be performed wherebythe Σ_(PL) values can be correlated back to the room temperature orstarting EQE (EQE can be measured using DeMello's method in anintegrating sphere). In other words, the Σ_(PL) at room temp is setequal to the room temp EQE, and then the % drop in Σ_(PL) at elevatedtemperatures, equates to an equivalent % drop from the room temperatureEQE value. (Σ_(PL) at RT is also referred to herein as I_(o), and Σ_(PL)at temperature T is also referred to herein as I(T).)

Example 6

FIGS. 3A and 3B graphically show a plot prepared from PL data measuredand collected for film samples described in Example 5. The data isplotted for ln [(Σ_(PL)(T=Room Temp)/Σ_(PL)(T))−1] vs. 1/k_(B)T wherek_(B) is Boltzmann's constant (in eV) to assess the multi-LO phononactivation energy. Table 2, below, lists the activation energy values(in eV) as determined from the graphs in FIGS. 3A and 3B.

TABLE 2 Table of Activation Energies: ACTIVATION ENERGY (EV) RED GREENCONTROL 0.38 0.38 IMPROVED 1.69 0.57

Example 7

FIGS. 4A and 4B provide the absorption spectra measured on samples ofsemiconductor nanocrystals of Examples 1A and 1B (identified in Table 3as “Improved”) and of Examples 2 and 3 (indentified in Table 3 as“Control”). The samples on which the measurements were taken wereprepared by diluting 5 microliters of the particular semiconductornanocrystal solution in 2.5 ml of solvent (hexane or toluene) such thatthe OD at 325 nm is less than 1. The spectrum of a sample is measured onthe sample in a 1 cm quartz cuvette by an Agilent Cary 5000 UV-Vis-NIRabsorbance spectrophotometer and normalized to the first excitonic peak.Table 3 below lists the Ratio of the absorption at 325 nm to theabsorption at 450 nm for the four samples.

TABLE 3 Table of Abs Ratios* (325/450 nm): ABS RATIO (325:450 NM) REDGREEN CONTROL 4.5 5.4 IMPROVED 7.8 17.4 *Abs Ratio can be the ratio ofOD or absorbance

Example 8 Control Sample (Red) Preparation of Semiconductor NanocrystalsCapable of Emitting Red Light Using 2 Step Nucleation and Growth CoreMethod and High Temperature No Amine Overcoat

Synthesis of CdSe Seed Cores:

45.94 mmol cadmium acetate is dissolved in 669.55 mmol oftri-n-octylphosphine at 100° C. in a 250 mL 3-neck round-bottom flaskand then dried and degassed for one hour. 814.69 mmol oftrioctylphosphine oxide and 104.85 mmol of octadecylphosphonic acid areadded to a 0.5 L stainless steel reactor and dried and degassed at 140°C. for one hour. After degassing, the Cd solution is added to thereactor containing the oxide/acid and the mixture is heated to 310° C.under nitrogen. Once the temperature reaches 310° C., the heating mantleis removed from the reactor and 139.9 mmol of diisobutylphosphineselenide (DIBP-Se) dissolved in 105 mL of 1-Dodecyl-2-pyrrolidinone(NDP) (1.5 M DIBP-Se) is then rapidly injected. The reactor is thenimmediately submerged in partially frozen (via liquid nitrogen) squalanebath rapidly reducing the temperature of the reaction to below 100° C.The first absorption peak of the nanocrystals is 476 nm. The CdSe coresare precipitated out of the growth solution inside a nitrogen atmosphereglovebox by adding a 3:1 mixture of methanol and isopropanol. Theisolated cores are then dissolved in hexane and used in a growth processto make red CdSe cores.

Growth of CdSe cores:

A 1 L glass reactor is charged with 320 mL of 1-octadecene (ODE) anddegassed at 120° C. for 15 minutes under vacuum. The reactor is thenbackfilled with N₂ and the temperature set to 60° C. 82 mL of the CdSeseed core above is injected into the reactor and the hexanes are removedunder reduced pressure until the vacuum gauge reading is <500 mTorr. Thetemperature of the reaction mixture is then set to 240° C. Meanwhile,two 50 mL syringes are loaded with 85 mL of cadmium oleate in TOP (0.5 Mconc.) solution and another two syringes are loaded with 85 mL ofdi-iso-butylphosphine selenide (DiBP-Se) in TOP (0.5 M conc.). Once thereaction mixture reaches 240° C., the Cadmium oleate and DiBP-Sesolutions are infused into the reactor at a rate of 40 mL/hr. Theexcitonic absorption feature of the CdSe cores is monitored duringinfusion and the reaction is stopped at 48 minutes when the absorptionfeature is 566 nm. The resulting CdSe cores are then ready for use as isin this growth solution for overcoating.

Synthesis of CdSe/ZnS/CdZnS Core-Shell Nanocrystals:

177 mL of the CdSe cores prepared as described in the precedingparagraph with a first absorbance peak at 566 nm are mixed in a 1 Lreaction vessel with 1-octadecene (137 mL), and Zn(Oleate)₂ (0.5 M inTOP, 54 mL). The reaction vessel is heated to 120° C. and vacuum isapplied for 15 min. The reaction vessel is then back-filled withnitrogen and heated to 310° C. The temperature is ramped, between 1°C./5 seconds and 1° C./15 seconds. Once the vessel reaches 300° C.,octanethiol (23 mL) is swiftly injected and a timer started. Once thetimer reaches 2 minutes, one syringe containing zinc oleate (0.5 M inTOP, 104 mL) and cadmium oleate (1 M in TOP, 85 mL), and another syringecontaining octanethiol (88 mL) are swiftly injected. Once the timerreaches 30 minutes, the heating mantle is dropped and the reactioncooled by subjecting the vessel to a cool air flow. The final materialis precipitated via the addition of butanol and methanol (4:1 ratio),centrifuged at 3000 RCF for 5 min, and the pellet redispersed intohexanes. The sample is then precipitated once more via the addition ofbutanol and methanol (3:1 ratio), centrifuged, and dispersed intotoluene for storage (26.9 g of core/shell material, 618 nm emission, 28nm FWHM, 93% quantum yield (QY), and 95% EQE in film).

Example 9

The EQE data presented in Table 4 and the related figure are calculatedbased on the integrated PL change with temperature and correlated backto the RT EQE. The integrated PL at RT is set equal to the RT measuredEQE and therefore any change in PL is then an equivalent % change in EQEwith adjustment for any absorption change at elevated temperatures.

The measurements used to calculate the values in Table 4 and the relatedfigure are based on a sample film prepared with the semiconductornanocrystals of the invention (the film being prepared as generallydescribed in Example 4 with nanocrystals prepared generally inaccordance with the procedure described in Examples 1A (red)) and acontrol film (the film being prepared as generally described in Example4 with nanocrystals prepared generally in accordance with the proceduredescribed in Example 8 (red)).

TABLE 4 EQE (%) v. Temperature (FIG. 7) Temperature (T) 20° 40° 60° 80°100° 120° 140° Sample C. C. C. C. C. C. C. Control (Red) 89 88 87 84 7970 60 Improved 95 95 95 95 94 94 91

FIG. 7 graphically depicts the calculated EQE values from Table 4 as afunction of temperature.

As can be seen in FIG. 7, the calculated EQE values for thesemiconductor nanocrystal of the present invention, as preferablyprepared in accordance with a method of the present invention are atleast 10% higher at room temperature (e.g., 20° C.-25° C.) than thecontrol (semiconductor nanocrystals of Example 8), with the differencebeing greater with increasing temperature. This also illustrates areduction in the quenching of semiconductor nanocrystal emission as afunction of temperature.

Table 5 below compares the Ratio of the absorption at 325 nm to theabsorption at 450 nm for the Improved samples of Example 7 with that fora control sample of semiconductor nanocrystals of Example 8.

TABLE 5 Table of Abs Ratios (325/450 nm): ABS RATIO (325:450 NM) REDGREEN CONTROL 4.25 (NONE) IMPROVED 7.8 17.4

As seen from the data presented in Table 6, Improved samples also show anotable increase in absorption (under excitation of 450 nm) at atemperature of 140° C. relative to the RT film absorption whereas thechange in absorption of the Control sample is notably less. (Acomparable change would be expected for the samples under excitation at<450 nm.)

TABLE 6 Absorption change at Temperature (%) Temperature Sample 25° C.140° C. Delta Control (Red) 86.85 87.17 0.32 Improved (Red) 65.92 68.282.36 Improved (Green) 79.81 83.19 3.38

In the attached Figures, information relating to a control sample islabeled “Standard” and information relating to a sample of an example ofan embodiment of the present invention is labeled “Improved”.

Example 10 Semiconductor Nanocrystals Capable of Emitting Green LightExample 10A Synthesis of CdSe Cores (448 nm Target)

The following are added to a 1 L steel reaction vessel:trioctylphosphine oxide (51.88 g), 1-octadecene (168.46 g),1-octadecylphosphonic acid (33.09 g, 98.92 mmol), and Cd(Oleate)₂ (1Msolution in trioctylphosphine, 98.92 mL, 98.92 mmol). The vessel issubjected to 3 cycles of vacuum/nitrogen at 120° C., and the temperatureis raised to 270° C. under nitrogen. At 270° C., a solution of 1Mdiisobutylphosphine selenide in N-dodecylpyrrolidone (DIBP-Se, 77.16 mL,77.16 mmol) is rapidly injected, within a period of less than 1 second,followed by injection of 1-octadecene (63.5 mL) to rapidly drop thetemperature to about 240° C. resulting in the production of quantum dotswith an initial absorbance peak between 420-430 nm. 5-20 seconds afterthe ODE injection, a solution of Cd(Oleate)₂ (0.5M in a 50/50 v/vmixture of TOP and ODE) is continuously introduced along with a solutionof DIBP-Se (0.4M in a 60/40 v/v mixture of N-dodecylpyrrolidone and ODE)at a rate of 29.0 mL/min. A total of 74.25 mL of each precursor isdelivered while the temperature of the reactor is maintained between205-240° C. At the end of the infusion, the reaction vessel is cooledrapidly by immersing the reactor in a squalane bath chilled with liquidnitrogen to rapidly bring the temperature down to <150° C. (within 2minutes). The final material is used as is without further purification(First absorbance peak: 448 nm, Total volume: 702 mL, Reaction yield:99%). The absorption spectrum of the core is shown in FIG. 8A.

Example 10B Synthesis of CdSe/ZnS/CdZnS Core/Shell/Shell

CdSe cores synthesized as described in the preceding paragraph, with afirst absorbance peak of 448 nm (27.70 mL, 4.78 mmol Cd), are mixed withdodecanethiol (23.76 mL, 99.20 mmol) in a syringe. A reaction flaskcontaining Zn(Oleate)₂ (99.20 mL, 0.5M in TOP) is heated to 300° C.,upon which the syringe containing cores and 1-dodecanethiol is swiftlyinjected. When the temperature recovers to 310° C. (between 2-8 min),the overcoat precursors are delivered via a syringe pump over a periodof 32 min. The two overcoating precursor stocks include thefollowing: 1) Zn(Oleate)₂ (141.25 mL, 0.5M in TOP, 70.63 mmol) mixedwith Cd(Oleate)₂ (79.64 mL, 1.0M in TOP, 79.64 mmol), and 2)dodecanethiol (39.59 mL, 165.29 mmol) mixed 1-octadecene (3.67 mL) andn-trioctylphosphine (0.92 mL). During the overcoating precursorinfusion, the temperature is kept between 320-330° C. Any volatiles fromthe system are allowed to distill over and leave the system in order forthe temperature to reach 320-330° C. After the infusion ends, the sampleis annealed for 3 minutes at 320-330° C. and cooled to room temperatureover a period of 5-15 minutes. The final core/shell material isprecipitated via the addition of butanol and methanol at a 2:1 ratiov/v. The pellet is isolated via centrifugation, and redispersed intotoluene for storage (Emission 531 nm, FWHM 41 nm, Film EQE at RT: 99%,Film EQE at 140° C.: >90%). Absorption and emission spectra of theresulting overcoated nanocrystals are shown in FIG. 8B.

Example 11 Semiconductor Nanocrystals Capable of Emitting Red LightExample 11a Synthesis of CdSe Cores

The following are added to a 1 L glass reaction vessel:trioctylphosphine oxide (15.42 g), 1-octadecene (ODE, 225.84 g),1-octadecylphosphonic acid (1.88 g, 5.63 mmol). The vessel is subjectedto 3 cycles of vacuum/nitrogen at 120° C., and the temperature is raisedto 270° C. under nitrogen. At 270° C., solutions of 0.25Mdiisobutylphosphine selenide in N-dodecylpyrrolidone (DIBP-Se, 17.55 mL,4.3 8 mmol) and 0.25M Cd(Oleate)₂ in trioctylphosphine/ODE (22.50 mL,5.62 mmol) are rapidly injected, within a period of less than 1 second,followed by injection of ODE (76.0 mL) to rapidly drop the temperatureto about 240° C., resulting in the production of quantum dots with aninitial absorbance peak between 420-450 nm. 5-20 seconds after the ODEquench, a solution of Cd(Oleate)₂ (0.5M in a 50/50 v/v mixture of TOPand ODE) is continuously introduced along with a solution of DIBP-Se(0.4M in a 60/40 v/v mixture of N-dodecylpyrrolidone and ODE) at a rateof 55.7 mL/hr. At 15 min, the infusion rate is increased to 111.4 mL/hr.At 25 min, the infusion rate is increased to 167.1 mL/hour. At 35 min,the infusion rate is increased to 222.8 mL/hr. At 45 min, the infusionrate is increased to 297.0 mL/hr. At 55 min, the infusion rate isincreased to 396.0 mL/hr. A total of 149.7 mL of each precursor isdelivered while the temperature of the reactor is maintained between215-240° C. At the end of the infusion, the reaction vessel is cooledusing room temperature airflow over a period of 5-15 min. The finalmaterial is used as is without further purification (First absorbancepeak: 576 nm, total volume: 736.5 mL, Reaction yield: 99%). Theabsorption spectrum of the core is shown in FIG. 9A.

Example 11B Synthesis of CdSe/ZnS/CdZnS Core/Shell/Shell

CdSe cores synthesized as described in the preceding paragraph, with afirst absorbance peak of 576 nm (90.10 mL, 8.70 mmol Cd), are mixed withZn(Oleate)₂ (47.62 mL, 0.5M in TOP, 23.81 mmol). The solution is heatedto 320° C., upon which a syringe containing 1-dodecanethiol (8.55 mL,35.7 mmol) is swiftly injected. After 10 min of annealing between305-325° C., the overcoat precursors are delivered via a syringe pumpover a period of 30 min. The two overcoating precursor stocks includethe following: 1) Zn(Oleate)₂ (89.73 mL, 0.5M in TOP, 44.87 mmol) mixedwith Cd(Oleate)₂ (104.68 mL, 1.0M in TOP, 104.68 mmol), and 2)dodecanethiol (70.59 mL, 294.70 mmol) mixed with 1-octadecene (21.29 mL)and TOP (5.32 mL). During the overcoating precursor infusion, thetemperature is kept between 320-330° C. Any volatiles from the systemare allowed to distill over and leave the system in order for thetemperature to reach 320-330° C. After the infusion ends, the sample isannealed for 5 min at 320-330° C. and cooled to room temperature over aperiod of 5-15 min. The final core/shell material is precipitated viathe addition of butanol and methanol at a 2:1 ratio v/v. The pellet isisolated via centrifugation, and redispersed into toluene (200 mL) forstorage (Emission 617 nm, FWHM 30 nm, Film EQE at RT: 92%, Film EQE at140° C.: 75-80%). Absorption and emission spectra of the resultingovercoated nanocrystals are shown in FIG. 9B.

The EQE values presented in the above Examples and related figures fortemperatures other than room temperature are relative values that arecalculated based on the integrated PL change with temperature andcorrelated back to the RT EQE. The integrated PL at RT is set equal tothe RT measured EQE and therefore any change in PL is then an equivalent% change in EQE with adjustment for any absorption change at elevatedtemperatures.

Semiconductor nanocrystals, compositions, optical components, devices,and other products described herein may be incorporated into a widevariety of other consumer products, including flat panel displays,computer monitors, all-in-one computers, notebooks, tablets,televisions, billboards, lights for interior or exterior illuminationand/or signaling, heads up displays, fully transparent displays,flexible displays, laser printers, telephones, cell phones, smartphones,personal digital assistants (PDAs), laptop computers, digital cameras,camcorders, viewfinders, micro-displays, vehicles, a large area wall,theater or stadium screen, a sign, lamps and various solid statelighting devices.

Semiconductors described herein can be excited optically and the opticalexcitation is downconverted via emission from the semiconductornanocrystals. Such photoluminescence is useful in any device/systemwhere a LED light source is used (e.g. solid-state lighting, LEDBacklights (LED-BLU) Liquid Crystal Displays (LCD)). Suchphotoluminescence can also be useful any device/system where a lightsource is downconverted to other wavelengths (e.g. solar concentratorsor downconverters where sunlight is converted to specific wavelengthstuned to highest efficiency window of the solar cells used in thesystem; plasma based systems where high energy plasma emission canexcite a semiconductor nanocrystal “phosphor”/downconverter; Taggants;bio-labeling or imaging; barcoding or security/covert labelingapplications).

Semiconductor nanocrystals described herein can also be excitedelectrically and the excitation results in emission from thesemiconductor nanocrystals. This process can involve: direct chargeinjection into the semiconductor nanocrystals generating semiconductornanocrystal excited states and subsequent semiconductor nanocrystalemission, or energy transfer from other semiconductor materials, forexample, within a device, to the semiconductor nanocrystals, generatingan excited state and subsequent semiconductor nanocrystal emission.

Semiconductor nanocrystals, compositions, optical components, and otherproducts described herein can also be useful in applications such as,for example, photovoltaic (PV) applications in which the semiconductornanocrystal materials are excited optically and the excitation resultsin current generation and/or a voltage due to carrier extraction fromthe semiconductor nanocrystals.

Additional information that may be useful in connection with the presentinvention and the inventions described herein is included inInternational Application No. PCT/US2009/002796 of Coe-Sullivan et al,filed 6 May 2009, entitled “Optical Components, Systems Including AnOptical Component, And Devices”; International Application No.PCT/US2009/002789 of Coe-Sullivan et al, filed 6 May 2009, entitled:“Solid State Lighting Devices Including Quantum Confined SemiconductorNanoparticles, An Optical Component For A Solid State Light Device, AndMethods”; International Application No. PCT/US2010/32859 of Modi et al,filed 28 Apr. 2010 entitled “Optical Materials, Optical Components, AndMethods”; International Application No. PCT/US2010/032799 of Modi et al,filed 28 Apr. 2010 entitled “Optical Materials, Optical Components,Devices, And Methods”; International Application No. PCT/US2011/047284of Sadasivan et al, filed 10 Aug. 2011 entitled “Quantum Dot BasedLighting”; International Application No. PCT/US2008/007901 of Linton etal, filed 25 Jun. 2008 entitled “Compositions And Methods IncludingDepositing Nanomaterial”; U.S. patent application Ser. No. 12/283,609 ofCoe-Sullivan et al, filed 12 Sep. 2008 entitled “Compositions, OpticalComponent, System Including An Optical Component, Devices, And OtherProducts”; International Application No. PCT/US2008/10651 of Breen etal, filed 12 Sep. 2008 entitled “Functionalized Nanoparticles AndMethod”; International Application No. PCT/US2009/004345 of Breen et al,filed 28 Jul. 2009 entitled “Nanoparticle Including Multi-FunctionalLigand And Method”, U.S. Patent Application No. 61/234,179 of Linton etal. filed 14 Aug. 2009 entitled “Lighting Devices, An Optical ComponentFor A Lighting Device, And Methods”; U.S. Patent Application No.61/252,743 of Linton et al filed 19 Oct. 2009 entitled “An OpticalComponent, Products Including Same, And Methods For Making Same”; U.S.Patent Application No. 61/291,072 of Linton et al filed 30 Dec. 2009entitled “An Optical Component, Products Including Same, And Methods ForMaking Same”; International Application No. PCT/US2007/024320 of Cloughet al, filed 21 Nov. 2007, entitled “Nanocrystals Including A Group IIIaElement And A Group Va Element, Method, Composition, Device And OtherProducts”; U.S. Pat. No. 6,600,175 of Baretz, et al., issued Jul. 29,2003, entitled “Solid State White Light Emitter And Display Using Same”;U.S. Pat. No. 6,608,332 of Shimizu, et al., issued Aug. 19, 2003,entitled “Light Emitting Device and Display”, and U.S. patentapplication Ser. No. 13/206,443 of Sadasivan et al. filed 9 Aug. 2011entitled “Quantum Dot Based Lighting”; each of the foregoing beinghereby incorporated herein by reference in its entirety.

As used herein, the singular forms “a”, “an” and “the” include pluralunless the context clearly dictates otherwise. Thus, for example,reference to a light emitting material includes reference to one or moreof such materials.

Applicants specifically incorporate the entire contents of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A semiconductor nanocrystal characterized byhaving a solid state photoluminescence external quantum efficiency at atemperature of 90° C. or above that is at least 95% of the solid statephotoluminescence external quantum efficiency of the semiconductornanocrystal at 25° C.; wherein the nanocrystal includes a corecomprising a first semiconductor material and a first shell surroundingthe core, wherein the first shell comprises a second semiconductormaterial and is disposed directly on the core, wherein the nanocrystalfurther includes a second shell surrounding the outer surface thereofand the second shell comprises a third semiconductor material, where thethird semiconductor material comprises a ternary mixture; and whereinthe semiconductor nanocrystal further includes a third shell, whereinthe third shell has a bandgap that is the same as that of the firstshell and the second shell has a bandgap that is less than that of thefirst shell.
 2. A semiconductor nanocrystal in accordance with claim 1wherein the temperature is in a range from 90° C. to about 200° C.
 3. Asemiconductor nanocrystal in accordance with claim 1 wherein thetemperature is in a range from 90° C. to about 140° C.
 4. Asemiconductor nanocrystal in accordance with claim 1 wherein thetemperature is in a range from 90° C. to about 120° C.
 5. Asemiconductor nanocrystal in accordance with claim 1 wherein the solidstate photoluminescence efficiency at the temperature of 90° C. or aboveis from 95 to 100% of the solid state photoluminescence efficiency at25° C.
 6. A semiconductor nanocrystal in accordance with claim 1 whereinthe first shell has a thickness greater than or equal to the thicknessof 1 monolayer of the second semiconductor material.
 7. A semiconductornanocrystal in accordance with claim 6 wherein the first shell has athickness up to the thickness of about 10 monolayers of the secondsemiconductor material.
 8. A semiconductor nanocrystal in accordancewith claim 1 wherein the second shell has a thickness greater than orequal to the thickness of 3 monolayers of the third semiconductormaterial.
 9. A semiconductor nanocrystal in accordance with claim 8wherein the second shell has a thickness up to the thickness of about 20monolayers of the third semiconductor material.
 10. A semiconductornanocrystal in accordance with claim 1 wherein the first shell compriseszinc sulfide, and the second shell comprises one or more metals whereinthe one or metals comprises from 0 to less than 100% cadmium.
 11. Asemiconductor nanocrystal in accordance with claim 1 wherein the corecomprises CdSe, the first shell comprises ZnS at a thickness of about3-4 monolayers of ZnS, and the second shell comprises Cd_(1-x)Zn_(x)Swherein 0<x<1 at a thickness of about 9-10 monolayers ofCd_(1-x)Zn_(x)S.
 12. A semiconductor nanocrystal in accordance withclaim 1 wherein first shell has a bandgap which is greater than that ofthe second shell.
 13. A semiconductor nanocrystal in accordance withclaim 1 wherein the first shell has a bandgap which is greater than thatof the second shell, and the bandgap of the first shell is also greaterthan that of the core.
 14. A semiconductor nanocrystal in accordancewith claim 1 wherein the first semiconductor material has a bandgapwhich differs from that of the second semiconductor material by at least0.8 eV.
 15. A semiconductor nanocrystal in accordance with claim 1wherein the first semiconductor material having a first conduction handenergy (E_(CB)), and the second semiconductor material having a secondconduction band energy (E_(CB)), and wherein the absolute value of thedifference between E_(CB) of the core and E_(CB) of the first shellmultiplied by the total shell thickness (nm) surrounding the core in thenanocrystal is greater than 2 eV*nm.
 16. A semiconductor nanocrystal inaccordance with claim 15 wherein the absolute value of the differencebetween E_(CB) of the core and E_(CB) of the first shell multiplied bythe total shell thickness (nm) surrounding the core in the nanocrystalis greater than 4 eV*nm.
 17. A semiconductor nanocrystal in accordancewith claim 1 wherein the first semiconductor material having a firstvalence hand energy (E_(VB)), and the second semiconductor materialhaving a second valence hand energy (E_(VB)), and wherein the absolutevalue of the difference between E_(VB) of the core and E_(VB) of thefirst shell multiplied by the total shell thickness (nm) surrounding thecore in the nanocrystal is greater than 2 eV*nm.
 18. A semiconductornanocrystal in accordance with claim 15 wherein the absolute value ofthe difference between E_(VB) of the core and E_(VB) of the first shellmultiplied by the total shell thickness (nm) surrounding the core in thenanocrystal is greater than 4 eV*nm.
 19. A semiconductor nanocrystal inaccordance with claim 1 wherein the first semiconductor material havinga first conduction band energy (E_(CB)), and the second semiconductormaterial having a second conduction band energy (E_(CB)), and whereinthe absolute value of the difference between E_(CB) of the core andE_(CB) of the first shell is at least 0.5 eV.
 20. A semiconductornanocrystal in accordance with claim 1 wherein the first semiconductormaterial having a first valence band energy (E_(CB)), and the secondsemiconductor material having a second valence band energy (E_(CB)), andwherein the absolute value of the difference between E_(VB) of the coreand E_(VB) of the first shell is at least 0.5 eV.
 21. A light-emittingdevice comprising a light-emitting element and an optical materialarranged to receive and convert at least a portion of light emitted byat least a portion of the light-emitting element from a first emissionwavelength to one or more predetermined wavelengths, wherein thematerial comprises a semiconductor nanocrystal in accordance with claim1.